Modification of the Spectral Absorption Characteristics of ZnGeP₂ in the THz and IR Wavelength Ranges Due to Diffusion Doping with Impurity Atoms of Mg, Se, Sn, and Pb

Abstract

This study demonstrates that diffusion doping of ZGP single crystals with impurity atoms (Mg, Se, Sn, Pb) leads to a decrease in the specific conductivity of the samples. Consequently, this results in reduced absorption in the terahertz frequency range (150–1000 μm). It has been shown that doping ZGP samples with selenium (Se) and lead (Pb) atoms reduces absorption in the infrared region from 0.3–0.6 cm⁻¹ to 0.06–0.09 cm⁻¹. Doping with tin (Sn) leads to a decrease in absorption only in the wavelength region near 2.1 μm from 0.2 cm⁻¹ to 0.05 cm⁻¹. The proposed mechanism for the decrease in infrared absorption is a reduction in zinc vacancies due to doping with impurity atoms. This research lays the groundwork for a technology that produces ZGP crystals with minimal absorption within the 2–8 μm wavelength range, eliminating the need for fast electron beam irradiation technology. This advancement will facilitate the fabrication of ZGP crystals with arbitrary apertures.

1. Introduction

Zinc Germanium Phosphide (ZGP) is a uniaxial, nonlinear positive crystal with a 42 m point group, a chalcopyrite-type crystal lattice, and a density of 4.12 g/cm³. Its Mohs hardness is 5.5. ZGP single crystals exhibit a high nonlinear susceptibility (d = 70 × 10⁻¹²–85.4 × 10⁻¹² m/V) and thermal conductivity (thermal conductivity coefficient of 36 W/(m·K)) [1]. The transmission range of the crystal extends from 0.74 to 12 μm [2]. However, the operational spectral interval of ZGP transmission, at an absorption coefficient level not exceeding ~1 cm⁻¹, is determined by wavelengths in the range of 0.9 to 8.3 μm. In the spectral range of 2.05–8.3 μm, ZGP has an absorption coefficient of ~0.02 cm⁻¹. Additionally, this crystal has a transparency window in the terahertz range [3].

Based on these nonlinear elements, parametric generators have been developed that produce radiation in the wavelength range of 3.5–5 μm with an average power of approximately 100 W and pulse energy of 200 mJ at pulse repetition rates of approximately 100 Hz to 100 kHz and pulse durations of approximately 10–30 ns, with a conversion efficiency of around 50% [4,5,6,7,8,9].

Additionally, ZnGeP₂ single crystals are used to generate sum and difference frequencies, as well as second harmonics of CO and CO₂ laser radiation [10,11] in the mid-infrared and terahertz ranges.

A promising direction is the creation of coherent terahertz radiation sources with a power of several milliwatts based on ZnGeP₂ elements using the generation of difference frequency radiation from infrared lasers [12]. Since ZnGeP₂ is used for nonlinear conversion of high-intensity laser radiation, it is necessary to optimize the processes of synthesis, growth, and post-growth treatments to obtain crystals with a high damage threshold, low absorption at the pump and generation wavelengths, and free from bulk defects. To achieve high efficiency in the frequency conversion process of radiation in nonlinear optical crystals, maximum transmission of pump and generated radiation and the highest possible pump radiation intensity are required. However, increasing this characteristic is limited by the optical damage threshold. Therefore, research aimed at reducing the absorption of ZGP in the anomalous absorption region is actively developing.

The absorption spectra of ZnGeP₂ crystals immediately after growth consist of two overlapping bands. The relatively high-energy band lies close to the fundamental absorption edge of ZnGeP₂ and contributes to optical losses at quantum energies exceeding 1.4 eV (<0.9 μm). The second, lower-energy band occurs in the spectral range of 0.9–2.5 μm (0.5–1.3 eV) and is the main obstacle to creating highly efficient parametric light generators pumped by radiation at a wavelength of ~2 μm [13]. Currently, a number of post-growth treatment methods for ZnGeP₂ have been developed that allow for a nearly tenfold reduction in ZnGeP₂ absorption in the wavelength range of ~1–2.5 μm.

Studies have shown that post-growth low-temperature (≤600 °C) treatment of ZnGeP₂ samples typically leads to a significant reduction in optical losses in the impurity absorption region [13]. It has been established that thermal annealing can reduce the optical absorption coefficient at λ~2 μm to approximately 0.1 cm⁻¹. At the same time, thermal treatment of ZnGeP₂ crystals did not lead to noticeable changes in the energy levels of optically active defects. The optical absorption coefficients for annealed ZnGeP₂ samples show that the detected optically active centers belong to the same deep donor levels as in crystals immediately after growth [13].

In [14], it is shown that along with the decrease in absorption, the dislocation density also decreases during low-temperature annealing, while the electrophysical characteristics of the crystals practically do not change. Obviously, all processes related to the formation and migration of point defects are practically excluded during low-temperature annealing, since the typical values of the diffusion coefficients of impurities and self-diffusion of components in wide-bandgap compounds at temperatures ~550 °C do not exceed 10–16 cm²/s, which gives very small diffusion lengths of point defects [14]. Thus, the change in the optical properties of ZnGeP₂ during low-temperature annealing is determined by the dislocation structure of the crystals, which allows explaining the boundaries of the temperature interval that ensures a noticeable improvement in the optical quality of the crystals. At temperatures less than 400–450 °C, dislocations are practically immobile, while at temperatures greater than 600 °C, the processes of dislocation generation prevail over the processes of their annihilation [14]. The clarification efficiency increases somewhat with an increase in the phosphorus pressure during low-temperature annealing [14]. The state of the surface layer provides the most favorable conditions for the movement of dislocations and their annihilation at a small excess of phosphorus vapor pressure (~2 atm) [14]. The absence of a direct correlation between the values of absorption (α) and dislocation concentration indicates that dislocations in this case play the role of a means, not a cause [14]. The movement of dislocations, causing structural rearrangements of atoms, affects very small second-phase inclusions or clusters of defects, for example, leads to the ordering of atoms in the cation sublattice of ZnGeP₂, i.e., to a decrease in the size of inclusions of the cubic β-phase of ZnGeP₂ [14].

In [15], the results of high-temperature annealing in vapors of volatile components are presented. From the thermodynamic analysis of the results of the influence of high-temperature treatment in vapors of volatile components on the electrophysical properties of ZnGeP₂, it is concluded that during high-temperature annealing, competing processes are observed that change the electrophysical parameters of crystals in different ways and proceed at different rates. High-temperature annealing has practically no effect on the magnitude of optical losses in ZnGeP₂ crystals since it is not possible to ensure that the composition of the crystal corresponds to the homogeneity region [14].

Under optimal conditions, irradiation with a fast electron beam leads to a decrease in absorption of ZnGeP₂ in the spectral range of wavelengths of 0.9–2.5 μm, in particular, at λ~2 μm, absorption decreases by an order of magnitude (from 0.1 cm⁻¹ to 0.01 cm⁻¹), but leads to an increase in absorption in the region λ < 0.9 μm [13]. The decrease in absorption in the region λ~0.9–2.5 μm is accompanied by significant changes in the energy spectra of optically active centers: deep-level donors with E = Ev + (0.85–0.90) eV disappear as the electron flux density increases and are replaced by defects with low-energy levels [13]. The increase in absorption in the region close to the fundamental absorption edge of 1.4–1.9 eV (0.7–1 μm) as a result of irradiation with a fast electron beam is associated with point defects formed during irradiation (vacancies or their complexes) [13,14]. In particular, in [16], a direct correlation was established between the intensity of optical absorption at a wavelength of 1 μm and the electron paramagnetic resonance signal associated with a singly ionized acceptor—zinc vacancy (VZn). Thus, the increase in optical absorption upon irradiation with a fast electron beam in the range of 1.4–1.9 eV (0.7–1 μm) can be attributed to the transitions V-Zn→EC or EV→V + P, which are also present in the crystal and contribute to the absorption of the material before irradiation (but their concentration before irradiation is lower) [13]. The low-energy optical absorption branch of 0.5–1.3 eV (0.9–2.5 μm) shows a tendency to decrease absorption upon irradiation and therefore cannot be associated with vacancies, the concentration of which increases during irradiation with a fast electron beam [13]. Thanks to low-temperature annealing of ZnGeP₂ samples irradiated with a fast electron beam, irreversible changes in absorption in the spectral range of 0.5–1.3 eV (0.9–2.5 μm) were found [13]. These changes are clearly visible both during isochronal and isothermal post-radiation annealing. These anneals reveal significant differences in changes in the optical spectra of irradiated ZnGeP₂ for high-energy and low-energy absorption bands. It can be seen that only radiation-induced defects (high-energy branch) are completely annihilated by recombination with excess vacancies introduced by irradiation [13]. In contrast, the absorption associated with the low-energy branch does not return to its original value. Thus, it can be seen that even at relatively low temperatures (180 °C), defects caused by irradiation have a bimolecular character and the interaction of defects plays an important role in post-radiation annealing processes [13]. The transformation of the absorption spectra of ZnGeP₂ upon irradiation with an electron beam and during post-radiation annealing is explained by the interaction of pre-existing point defects with those induced by irradiation [13]. This fact is in good agreement with the Nelson model known in radiation physics, according to which the dissolution of small inclusions in crystals is possible due to the interaction of inclusion atoms with vacancies generated in the crystal matrix under conditions of high-intensity irradiation. When considering possible interactions between the initial defects in ZnGeP₂ and vacancies formed during irradiation with an electron beam, it is noted in [13] that disorder defects (Ge→Zn and Zn→Ge) are responsible for optical absorption in ZnGeP₂ in the spectral range of 0.5–1.3 eV (0.9–2.5 μm) and can interact with radiation-induced defects in two ways, one of which is irreversible. Such an interpretation is in good agreement with both the sequential “disappearance” of optically active defects with an energy position of E = Ev + (0.85–0.90) eV and with the shift of the energy level with an increase in the electron beam flux density. Both reversible (electrical) and irreversible (chemical) defect interactions reduce the concentration of absorbing centers during irradiation; the concentration can only be partially restored during post-radiation annealing [13].

Thus, the use of various post-growth treatments allows for the improvement of the optical quality of ZnGeP₂ crystals, in particular, reducing absorption by an order of magnitude at wavelengths in the 2-micron region.

In work [17], using terahertz spectroscopy methods, it was shown that the absorption of ZnGeP₂ in the terahertz spectral range of 300–1000 μm is diffuse in nature; that is, it does not have pronounced resonances over a wide frequency range. Due to this fact, it was suggested that free carriers play a decisive role in the formation of dielectric losses in this frequency range. Studies conducted with a variable concentration of free charge carriers under the influence of fast electrons and changing temperature conditions [18,19] showed the absence of a noticeable effect of temperature (from 300₀ to 20₀ K) on the optical parameters of crystals and the absence of a pronounced correlation with post-growth treatment conditions (annealing at 600 °C). In [20], dispersion dependences of the refractive index and absorption coefficient of the studied ZnGeP₂ samples were obtained at wavelengths of 300–1000 μm in the region of fundamental absorption. It is shown that the presence of bulk inclusions in a single crystal leads to an increase in the refractive index and absorption in the entire studied terahertz range. In work [21], dispersion relations were studied in combination, and at the same time, the parameters of inclusions in the crystal were measured using IR digital holography.

Until recently, the effect of doping with various chemical elements on the optical characteristics of ZGP (in particular, on reducing absorption in the IR and THz ranges) was not adequately studied. In [14], ZGP was doped with the chemical element Mn, resulting in a new ferromagnetic material, ZnxMn1–xGeP₂, but no studies were conducted on the systematic study of the effect of doping on the optical properties of crystals in the IR and THz wavelength ranges. In addition, in [15], studies were conducted on the effect of diffusion doping with a copper impurity on the electrophysical properties of ZGP crystals. As these studies have shown, doping with Cu by diffusion annealing is an effective way to vary the hole concentration within 10¹²–10¹⁶ cm⁻³ in ZGP due to the acceptor nature of the introduced Cu defects, although studies of the effect of doping on optical properties were also not conducted; however, in the last few years, interest in this area of research has grown significantly. A number of studies have been conducted, showing the promise of the approach of doping ZnGeP₂ single crystals to modify their optical properties in the THz range and in the IR range.

In [22], the effect of doping ZnGeP₂ with Mg, Se, and Ca via diffusion on the optical damage threshold at a wavelength of 2.1 μm was studied. It was shown that diffusion doping with Mg and Se leads to an increase in the laser-induced damage threshold (LIDT) of the ZnGeP₂ single crystal; with annealing at a temperature of 750 °C, the damage threshold of samples doped with Mg and Se increases by 31% and 21%, respectively, from 2.2 ± 0.1 J/cm² to 2.9 ± 0.1 and 2.7 ± 0.1 J/cm², respectively. When ZnGeP₂ is doped with Ca, the opposite trend is observed. It was suggested that changes in LIDT depending on the introduced impurity by diffusion can be explained by the creation of additional energy scattering channels due to processes of radiative and fast non-radiative relaxation through impurity energy levels, which requires further experimental confirmation. In [15], a correlation was also observed between the optical damage threshold and the electrophysical parameters of the crystals after doping, in particular, with the conductivity of the samples. A decrease in conductivity is observed when ZGP samples are doped with Mg and Se, and when doped with Ca, the conductivity of ZGP increases compared to an undoped annealed sample. The conducted studies have shown that the technological possibility of increasing the LIDT of ZGP crystals can be realized by reducing the conductivity of the samples through controlled doping. The absorption spectra of ZGP samples doped with Mg, Se, and Ca atoms by diffusion were measured in the terahertz spectral range (100–1000 μm). The assumption that the absorption spectrum of ZGP in this range is determined by the concentration of free charge carriers is confirmed. As the conducted studies have shown, samples doped with Mg and Se demonstrate a decrease in specific conductivity compared to an undoped ZGP sample, which leads to a decrease in absorption in the THz range. In [23], the issue of introducing a donor impurity Se into a ZGP single crystal was studied. It was shown that doping with Se leads to the minimization of undesirable optical absorption from singly ionized zinc vacancies, which shows the promise of doping with Se to reduce optical absorption in the region of anomalous absorption of ZGP. In [24], doping of ZGP crystals with tin (Sn) led to a 40% reduction in absorption in the wavelength region near 2 μm. In [24], it was shown that the decrease in absorption in the wavelength region near 2 μm due to the sequential combination of doping with Sn at the synthesis stage, annealing, and electron irradiation is apparently due to obtaining single crystals of large sizes with the least content of zinc vacancies. These processes allowed for the reduction of the content of zinc vacancies in the crystal by about 90% compared to the material grown without Sn.

This paper presents the results of studies on the effect of doping ZGP crystals with Pb and Sn impurity atoms on the optical properties of the crystal in the THz and IR wavelength ranges, and the obtained results are generalized together with the results obtained by us earlier on doping ZGP crystals with Mg and Se in [22].

2. Methodology for Measuring Absorption Coefficient in the THz and IR Ranges and Electrophysical Parameters of ZGP

A ZGP single crystal grown by the vertical Bridgman method on an oriented (100) seed was used, from which 7 samples with a (100) orientation and dimensions of 6 × 6 × 2.45 mm³ were cut. The working surfaces of the samples were polished after gluing them into a block using the standard technology described in [22] on a 4-PD-200 polishing and grinding machine. The surface roughness of the samples was measured on the 3D optical profilometer MicroXAM-800 (KLA-Tencor, Milpitas, CA, USA). For all samples, the PSI phase mode and Nikon X50 objective (Tokyo, Japan) were used. The field of view was 116 μm × 152 μm. The roughness parameters for the polished surfaces of all samples were Rz = 1.7 nm, Ra = 0.24 nm, and Rq = 0.31 nm. An example of the roughness profile is shown in Figure 1.

On the pre-polished faces of the samples, the following chemical elements were thermally sprayed: Pb and Sn (the thickness of the sputtered film was 1.5 μm). After that, the ZGP samples with the deposited films and two control samples without sputtering were annealed in a quartz-sealed evacuated ampoule, into which a phosphorus charge was added to create a pressure of 4 atm in the ampoule when the operating temperature was reached. The annealing of the samples was carried out at a temperature of 650 °C for one set of samples and 750 °C for another similar set for 200 h. After the diffusion doping, the working surfaces of the studied samples were re-polished.

Since the doping of the samples was carried out by diffusion from the crystal surface, the concentration distribution of the doping impurity had an exponential dependence on depth. However, this experimental approach proved sufficient to detect the influence of the impurity on the optical properties of ZGP crystals in the IR and THz spectral ranges. In the future, it will be necessary to conduct studies with bulk doping of crystals with these impurity atoms to obtain the required impurity concentrations throughout the crystal volume.

Further, the specific conductivity of the ZGP samples was measured by the Van der Pauw method [25]. The transmission of the samples in the wavelength range of 0.6–12 μm was recorded using a Shimadzu UV-3600 spectrophotometer and a Simex Fourier spectrophotometer.

Absorption in the IR spectral region in crystals, taking into account multiple reflections from the parallel faces of the studied samples, was determined using the formulas in [26].

$${\alpha }^{e,o}=-{\displaystyle \frac{1}{d}}\ln (\sqrt{{(A}^2+{\left(R^{e,o}\right)}^{-2})}-A)$$

(1)

$$R^{e,o}={\displaystyle \frac{{(n^{e,o}-1)}^2}{{(n^{e,o}+1)}^2}}$$

(2)

$$T^{e,o}={\displaystyle \frac{I^{e,o}}{I_o}}={\displaystyle \frac{{(1-R^{e,o})}^2{e}^{(-{\alpha }^{e,o}d)}}{{(1-R^{e,o})}^2{e}^{(-{2\alpha }^{e,o}d)}}}$$

(3)

$$T={\displaystyle \frac{I}{I^o}}={\displaystyle \frac{T^o}{2}}\left[1+{\cos }^2\left(\theta \right)\right]+{\displaystyle \frac{T^e}{2}}{\cos }^2\left(\theta \right)$$

(4)

where α^e,o—absorption coefficient for the ordinary and extraordinary waves, respectively. This measures how strongly the material absorbs light. d—thickness of the plate. This is a simple geometric parameter. R^e,o—reflection coefficient for the ordinary and extraordinary waves, respectively. This indicates the fraction of light that is reflected from the surface. n^e,o—refractive index for the ordinary and extraordinary waves, respectively. This is a measure of how much the speed of light is reduced inside the material. θ—angle between the direction of radiation (or wave vector) and the optical axis of the crystal. This angle determines how the anisotropic properties of crystal affect the light. T^e,o—transmittance for the ordinary and extraordinary rays, respectively. This is the fraction of light that passes through the material. I^e,o—intensity of the ordinary and extraordinary rays, respectively. This measures the power of the light. I^o—intensity of the radiation incident on the single crystal. This is the initial light intensity before it interacts with the crystal. T—transmittance of the sample. This is the overall fraction of light that passes through the sample.

Absorption in the THz wavelength range was measured using a pulsed time-domain terahertz spectrometer, the setup of which is shown in Figure 2. The principle of operation of this spectrometer is detailed in [27,28]. A beam splitter (BS) is used to split the femtosecond laser radiation with a duration of 100 fs at a central wavelength of 780 nm, which is carried out using a Mai Tai SP laser (Spectra Physics, Milpitas, CA, USA), generating a laser pulse with a power of about 97% of the pump beam power and 3% of the probe beam power. Terahertz pulses were generated in a 790 μm thick GaSe crystal using type-eee conversion [26,27].

To register the pulse that passed through the studied ZGP sample, a 1100 μm thick ZnTe electro-optic crystal was used.

3. Experimental Results and Discussion

Table 1. Conductivity of the studied samples and optical breakdown threshold parameters.

Dopant	σ, 1/Ω∙cm
Mg	5.42 × 10−6
Se	4.16 × 10−7
Sn	5.88 × 10−8
Pb	6.09 × 10−8
Without Dopant	1.24 × 10−6

presents the results of determining the specific conductivity of ZGP samples doped with various impurity atoms. The values for samples doped with Mg and Se are taken from [22].

As the table shows, the provided data indicate that the doped samples conduct electricity less well than the undoped ZGP sample. However, the sample doped with magnesium exhibited almost no change in conductivity compared to the undoped sample. The conductivity of samples doped with selenium decreased by nearly one order of magnitude. Samples doped with tin and lead showed an even more significant decrease in conductivity, nearly two orders of magnitude. Considering the results presented in [22], we expect that samples doped with lead and tin will exhibit reduced absorption in the terahertz region of the spectrum.

In work [17], terahertz spectroscopy methods showed that ZnGeP₂ absorption in the terahertz spectral range of 300–1000 μm is diffuse, meaning it lacks pronounced resonances over a wide frequency range. This indicates that free charge carriers play a key role in forming dielectric losses in this frequency range. Consequently, a decrease in the conductivity of a ZGP single crystal should lead to a decrease in absorption in the wavelength range of 300–1000 μm. In work [22], it was shown that doping a ZGP crystal with Mg and Se impurity atoms leads to an increase in conductivity and, consequently, to an increase in transmittance in the THz wavelength range (150–1000 μm). Thus, after observing that doping a ZGP crystal with Sn and Pb atoms also leads to an increase in the conductivity of the samples, we hypothesized that this could also lead to an increase in transmittance in the THz wavelength range, which was demonstrated by the absorption spectra of the doped samples presented in Figures 7 and 8.

Figure 3, Figure 4, Figure 5 and Figure 6 present the infrared absorption spectra (1.5–12 μm) of ZGP samples diffusion-doped with magnesium, selenium, tin, and lead at temperatures of 650 °C and 760 °C. These spectra are compared to those of ZGP samples annealed at the same temperatures but without any doping.

As can be seen from Figure 3, diffusion doping with Mg into ZGP single crystals does not lead to significant changes in the transmission spectrum of the crystals compared to undoped samples. A slight decrease in absorption in the wavelength range of 2.5–8 μm is observed when annealing at a temperature of 750 °C.

Figure 4 shows that doping ZGP with selenium impurity atoms at an annealing temperature of 650 °C leads to a nearly tenfold decrease in absorption in the wavelength range of 2.1–8 μm compared to the undoped sample, from 0.5 cm⁻¹ to 0.06 cm⁻¹. At the same time, annealing the sample at a temperature of 750 °C leads to a relaxation of the absorption values to the level of the undoped sample, except for the wavelength range of 5.7–6.5 μm.

Doping ZGP with impurity atoms of Pb at an annealing temperature of 650 °C and 750 °C leads to a decrease in absorption in the wavelength range of 2.1–8 μm, as shown in Figure 5, similar to the case of doping with Se at a temperature of 650 °C, by almost an order of magnitude compared to the undoped sample, from 0.5–0.3 cm⁻¹ to 0.06–0.09 cm⁻¹.

Figure 6 shows that doping with tin does not lead to significant changes in the majority of the measured absorption spectrum of ZGP samples. However, a significant decrease in absorption is observed in the wavelength region of ~2.1 μm when doped with Sn, from 0.2 cm⁻¹ to 0.05 cm⁻¹. This result is a direct confirmation of the data recently obtained in [24] indicating that Sn doping of ZGP leads to a significant decrease in the concentration of Zn vacancies in the single crystal.

As previously shown in [22], the absorption spectra of ZGP in the wavelength range of 150–1000 μm at annealing temperatures of 650 °C and 750 °C do not differ significantly. Therefore, in Figure 7 and Figure 8, the comparison of the absorption spectra of doped samples is carried out only using spectral data obtained from an undoped ZGP sample annealed at a temperature of 650 °C. The article presents the absorption spectra in the THz wavelength range for ZGP samples doped with impurity atoms of Sn and Pb. The THz absorption spectra for ZGP samples doped with Mg and Se are given in [22].

The obtained data show that after doping samples with Sn and Pb atoms, a decrease in absorption by about 1.5 cm⁻¹ is observed across the entire measured spectral range at annealing temperatures of 650 °C and 750 °C. Similar dependences were obtained in [22] for ZGP samples doped with impurity atoms of Mg and Se. As the research results showed, samples doped with Mg, Se, Sn, and Pb demonstrate a decrease in specific electrical conductivity compared to the undoped ZGP sample, which leads to a decrease in absorption in the THz range, which is in good agreement with the results of works [18,19,20].

4. Conclusions

The conducted research has demonstrated the technical feasibility of reducing absorption in ZGP single crystals in the IR and THz spectral regions by doping them with impurity atoms of Mg, Se, Sn, and Pb.

It has been shown that diffusion doping of ZGP single crystals with impurity atoms of Mg, Se, Sn, and Pb leads to a decrease in the specific conductivity of the samples, which in turn leads to a decrease in absorption in the THz spectral region (150–1000 μm) since the main mechanism responsible for absorption in this spectral region is absorption by free charge carriers. Consequently, a decrease in the concentration of free charge carriers due to doping leads to a decrease in absorption by ~1.5 cm⁻¹.

It has been shown that doping ZGP samples with impurity atoms of Se and Pb leads to a decrease in absorption in the IR wavelength range from 0.3–0.6 cm⁻¹ to 0.06–0.09 cm⁻¹. Doping with Sn leads to a decrease in absorption only in the wavelength region near 2.1 μm from 0.2 cm⁻¹ to 0.05 cm⁻¹. The proposed mechanism for the decrease in absorption in the IR spectral region is a decrease in Zn vacancies due to doping with impurity atoms, which is in good agreement with the results obtained in [24]. It should be noted that doping ZGP single crystals with impurity atoms of Se and Pb made it possible to obtain crystals with absorption in the IR spectral region, especially near the wavelength of 2.1 μm, comparable to crystals subjected to irradiation with a fast electron beam. In the future, this will make it possible to create a technology for producing ZGP crystals with minimal absorption in the wavelength range of 2–8 μm without using irradiation technology with a fast electron beam. This will allow the creation of ZGP crystals of arbitrary aperture. Currently, the aperture of nonlinear ZGP elements from a number of manufacturers is determined by the power of fast electron sources and does not exceed 6 mm on the side of the crystal subjected to irradiation. The advantages of the developed technology include the simultaneous reduction of absorption in both the IR and THz parts of the spectrum.