No 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.

Using a quasichemical approach, the total native defect concentration and the minimum deviation in stoichiometry have been calculated in CdTe crystals as a function of the Cd pressure at various temperatures. With this knowledge, CdTe and (Cd,Zn)Te wafers have been subjected to postgrowth step annealing treatment under conditions such that the crystals are in equilibrium with a Cd or (Cd,Zn) vapor corresponding to the minimum in deviation from stoichiometry at each annealing temperature. The step annealed CdTe and (Cd,Zn)Te wafers have been examined under infrared microscopy and have shown significant reduction in the concentration of Te precipitates, whereas the unannealed wafers have had numerous Te precipitates distributed throughout the bulk. HgCdTe epitaxial films have been grown on the step annealed CdTe and (Cd,Zn)Te wafers as well as on unannealed wafers from the same boule. Examination of the cross sections of the epitaxial films indicates appearance of Te precipitates in films grown on unannealed substrates, whereas no Te precipitation was evident in films grown on the annealed substrates leading to the inference that the occurrence of Te precipitates in the (Hg,Cd)Te films is possibly related to the presence of Te precipitates in the substrates. Thermal migration of Te under a temperature gradient during step annealing is suggested as a possible mechanism in the elimination of larger size Te precipitates whereas the extremely fine precipitates (<1 μm) appear to need in-diffusion of metal vapor for their elimination.

The results of arsenic incorporation in HgCdTe layers grown by molecular beam epitaxy (MBE) are reported. Obtained results indicate that arsenic was successfully incorporated as acceptors in MBE-HgCdTe layers after a low temperature anneal. Secondary ion mass spectrometry and Hall effect measurements confirm that arsenic is incorporated with an activation yield of up to 100%. This work confirms that arsenic can be used as an effective dopant of MBE-HgCdTe after a low temperature annealing under Hg-saturated conditions.

Se was diffused into Si doped with various concentrations of the group-III elements B, Ga, Al, or In. Selenium acting as a double donor in silicon is found to pair with all the acceptors from the group-III examined, and the Se-acceptor pairs give rise to a donor level at Ec−0.2 eV. An additional donor level at Ec−0.3 eV is assigned to the first ionization level of selenium in silicon. Solubility of Se in silicon in the temperature range 850–1300 °C has been established through Hall-effect measurements. The diffusion coefficient measurements between 800 and 1250 °C yielded 2.47 exp(−2.84 eV/kT) cm2/sec for the diffusion coefficient of Se, DSe.