Lattice Defects in Semiconducting Hg1 − x Cd x Te Alloys: I . Defect Structure of Undoped and Copper Doped

Abstract

Undoped Hg0.8Cd0.2normalTe crystals were subjected to high temperature equilibration at temperatures ranging from 400° to 655°C in various Hg atmospheres. Hall effect and mobility measurements were carried out on the crystals quenched to room temperature subsequent to the high temperature equilibration. The variation of the hole concentration in the cooled crystals at 77 K as a function of the partial pressure of Hg at the equilibration temperatures, together with a comparison of the hole mobility in the undoped samples with that in the copper‐doped samples, has yielded a defect model for the undoped Hg0.8Cd0.2normalTe crystals, according to which, the undoped crystals are essentially intrinsic at the equilibration temperatures and the native acceptor defects are doubly ionized. Native donor defects appear to be negligible in concentration, implying that the p‐to‐n conversion in these alloys is mainly due to residual foreign donor impurities. The thermodynamic constants for the intrinsic excitation process as well as for the incorporation of the doubly ionized native acceptor defects in the undoped crystals have been arrived at. Copper appears to be incorporated on metal lattice sites acting as a single acceptor with little compensation. Results on the heavily copper‐doped samples indicate that the quench from the equilibration temperatures was imperfect resulting in a large fraction of the copper precipitating during the quench. From results of experiments where the cooling rate from the equilibration temperatures was intentionally varied in the undoped samples, a qualitative correlation was established between the quenching efficiency and the presence of macroscopic defects such as voids and inclusions in the samples.

Reaction constants for main cationic native defects in narrow-gap Hg1−Cd Te crystals

“…1 Te-saturated (3,4) conditions. Points-the experimental data for V Hg in the p-type samples (1,3) or in the n-type samples (2, 4) and for Hg I (5); solid lines-the results of the calculations for V Hg at Hg saturation (1 ) or at Te saturation (3 ) and for Hg I at Hg saturation (5 ); broken lines 6, 7-the data from [2] for V Hg at Hg and Te saturation, respectively; broken lines 8, 9-the data from [11] for, respectively, V Hg and Hg I at Hg saturation. acceptor energy:…”

“…It is well known, that mercury vacancies V Hg and mercury interstitials Hg I are the main such defects in MCT crystals [1][2][3], and that there are still some characteristics of these defects, which have to be studied. For example there are no reliable experimental data about vacancy ionization degree in MCT.…”

“…For example there are no reliable experimental data about vacancy ionization degree in MCT. It is usually considered that the vacancies are doubly ionized at 77 K [2], but this is doubtful because the vacancy ionization energy is too large (>16 meV [4]). Therefore, the main task of the investigations was to determine in detail the real vacancy ionization degree at T = 77 K depending on vacancy concentration and on this basis to obtain reliable reaction constants for mercury vacancies and interstitials in the narrow-gap MCT crystals.…”

IR Materials Producibility.

“…Shown for comparison are the experimental data from Vydyanath. 1 In the calculations, we allowed both atomic and electronic equilibrations at the high temperature at which the annealing takes place; we then assume the total defect concentrations are frozen-in upon quenching,…”

Low-temperature annealing of (Hg,Cd)Te

“…This parameter is equal to the concentration of doubly ionized metal vacancies, VЈЈ, in the alloy as required by mass balance. 2 When this vacancy concentration is significantly smaller than the intrinsic-carrier concentration, which appears to be valid for most anneal conditions for HgCdTe alloys with low x values, the alloy will be intrinsic during the anneal, 9 and the vacancy concentration under tellurium-saturated conditions would follow a behavior described by 1…”