**LWIR Photodiodes and Focal Plane Arrays Based on Novel HgCdTe/CdZnTe/GaAs Heterostructures Grown by MBE Technique**

V. V. Vasiliev, V. S. Varavin, S. A. Dvoretsky, I. M. Marchishin, N. N. Mikhailov, A. V. Predein, I. V. Sabinina, Yu. G. Sidorov, A. O. Suslyakov and A. L. Aseev

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/50822

## **1. Introduction**

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Thermal imagers based on the photo detectors for infrared (IR) wavelength range of 3–12 μm are required for applications both in the military equipment for systems of night vision, detection and guidance as well as in the national economy for the medical, agricultural, chemical, metallurgical, fuel industries and others. Nowadays, the leading place among ma‐ terials for the production of IR photo detectors is occupied by mercury–cadmium–telluride (MCT) solid solutions. This fact is due to the physical properties of these solutions (high speed, the possibility of varying an MCT band gap within a wide range, and high quantum efficiency in the range of overlapping wavelengths). For the last 25 years, the technology of MCT production has been developed intensively, which has made it possible to pass from manufacturing bulk single crystals of relatively small diameters (less than 10 mm) to epilay‐ ers on large in diameter substrates (up to 150 mm). The MCT epilayers on large-diameter substrates are necessary for the production of IR PD arrays with a large number of elements for enhancing the production efficiency and reducing the cost of devices. According to this, stringent requirements are imposed on the epitaxial technologies of producing such an MCT material. They include a high structural quality and uniformity of photoelectric characteris‐ tics over the entire area. MCT layers on alternative substrates primarily due to its low growth temperatures (~180 ºC), which prevents the diffusion of impurities from the sub‐ strate and reduces the background doping with these impurities. The great successes had

© 2012 Vasiliev et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 Vasiliev et al.; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

been reached in development of growth MCT HES by MBE on GaAs and Si large in diame‐ ter substrate. The decision of fundamental physical and chemical investigations and techno‐ logical developments allows to fabricate high quality MCT HES on GaAs substrate. Such MCT HES are widely used for developments and production of different formats linear and matrix IR detectors sensitive in separate spectral IR ranges.

For this purpose the preepitaxial substrate surface preparation included the chemical etch‐

LWIR Photodiodes and Focal Plane Arrays Based on Novel HgCdTe/CdZnTe/GaAs Heterostructures Grown by MBE

We used (013)GaAs substrates 2" and 3" in diameter which initially prepared as epiready. Nevertheless it is necessary to remove the defects surface layer which prevents the epitaxial growth of high quality MCT HES. The study of chemical etching of GaAs in sulfuric acid etch‐ ant [1] allows to determine optimal conditions for preparation GaAs surface. Fig. 2 represents the density of luminous points which appeared after chemical etching of GaAs substrates [2].

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http://dx.doi.org/10.5772/50822

135

ing process and thermal cleaning process in ultra-high vacuum at 500600 0

**Figure 2.** The dependence of number luminous points on etching depth (013) GaAs.

chiometric surface with elemental arsenic coating.

ing in H2SO4/ H2O2/H2O (3:1:1) mixture at 35-40 0

ing HCl solution in isopropyl alcohol during 10 min.

mation elemental arsenic coating.

It is clear that the density of luminous point changes with etching depth increases more that one order of magnitude from initial values reaches maximum at 10-15 μm. So we deter‐ mined the optimal etching depth for epitaxial growth MCT HES which is equal to ~20 μm. It was determined that carbon contamination does not evaporate at thermal treatment in ul‐ tra-high vacuum. The presence of 0,06 monolayer carbons coating on the GaAs surface is disturb epitaxy [3-5]. It necessary to create a continence protective layer more than monolay‐ er thickness which must not adsorbs carbon and desorbs at low temperatures. It was found by SIMS that at treatment of etching GaAs surface in HCl solution in spirit lead to decrease of carbon on the surface less 0.5 % monolayer [6]. At this procedure the arsenic oxides and gallium oxides were removed at room temperature from the GaAs substrate leading to stoi‐

We used the procedure of final etching in boiling HCl solution in isopropyl alcohol for for‐

So, the chemical procedure of GaAs surface preparation before the growth includes the etch‐

C during 6-10 min. and final and in boil‐

In this chapter the results of studies of technological processes at growth MCT HES on (013)GaAs by MBE, the developments of HES design and fabrication on its basis of high quality IR detectors of different applications for IR radiation registration in spectral long wavelength range (LWIR) 8-11 μm.
