摘要:

The results of a systematic study of low temperature diffusion of indium and arsenic under Hg‐saturated conditions in HgCdTe epilayers grown by molecular‐beam epitaxy (MBE) are reported. Anneal temperatures ranging from 250 to 400 °C were investigated. To our knowledge, this is the first report of indium and arsenic diffusion coefficients at temperatures less than 300 °C. Indium was determined to be more stable to redistribution than arsenic in the MBE layers at the temperatures investigated. During this study, evidence ofp‐type impurity outdiffusion from the substrate during anneal was discovered. Both copper and silver were observed to segregate into the HgCdTe epilayer during anneal. This latter effect represents a critical problem in the use of CdTe and CdZnTe substrates for material growth, and may be a major factor limiting yield of material and devices.

ISSN:1071-1023    

DOI:10.1116/1.586268

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

Several aspects concerning the role of point defects and defect–impurity interaction in II–VI semiconductors are reviewed. First, the properties of the cation vacancy in CdxHg1−xTe are re‐examined in the light of two experiments (mass‐loss measurements, positron lifetime) which point out to a large concentration of vacancy‐type defects compared to the hole carrier density. The possibility for the cation vacancy to be a negative‐Ucenter and the formation of divacancies are discussed. Second, the case of donor‐vacancy pairs is considered. A model of impurity compensation is given which accounts for the doping limits observed in a number of semiconductors in terms of a fundamental energy parameter (dangling bond energy).

ISSN:1071-1023    

DOI:10.1116/1.586269

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

The motion of dislocations in crystals is known to be impeded by the addition of isovalent impurities at concentrations of a few percent. By treating the Hg1−xCdxTe alloy as resulting from the addition of Cd impurities into the HgTe lattice, the critical resolved shear stress for solid‐solution hardening in this material is calculated at room temperature as a function of Cd compositionx. In this solid solution model, the critical stress is derived from the elastic size interaction between the Cd solute atoms and the edge dislocations in a HgTe solvent. The predicted dependence of the critical stress onxat room temperature compares favorably with experimental results for the lower yield stress. Estimates of the critical stress at temperatures up to 440 °C are also made at selected compositions by using the relation for the temperature and strain rate dependence of the lower yield stress.

ISSN:1071-1023    

DOI:10.1116/1.586270

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

The microhardnesses of HgCdTe, HgZnTe, and HgCdZnTe are calculated using a formalism which combines a solid‐solution hardening model, an analysis of the composition dependence of the critical stress, and an empirical relation between critical stress and microhardness. Reasonable agreement with available data is obtained for the magnitude of the hardness and its variation with composition in HgCdTe and HgZnTe. In qualitative agreement with previous studies of the lattice strengthening effects of Zn on HgTe and HgCdTe, it is found that the alloys containing Zn have larger hardnesses than HgCdTe for all compositions. Another interesting result is that, for simultaneous variations of the Cd and Zn compositions in HgCdZnTe that leave the band gap fixed in the infrared, the microhardness is between those of HgZnTe and HgCdTe, and it varies almost linearly with Zn composition.

ISSN:1071-1023    

DOI:10.1116/1.586271

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

Ion milling, a process believed to introduce interstitial mercury deeply into and type convert vacancy‐dopedp‐HgCdTe, is shown to produce long‐range isotropic damage inn‐Hg1−xCdxTe (x=0.22). This damage is characterized by a bias‐dependent dark current in metal–insulator semiconductor devices. Previous work has shown that ion milling also produces a moderate reduction in photoconductive response, a few micrometers below the ion‐milled surface without reducing minority‐carrier lifetime, and this is also presented here. It is determined that the severity of ion‐mill damage can be reduced with a bake, either at 100 or 185 °C. The thermal decomposition of an anodic oxide, which is also believed to introduce interstial mercury deeply into and type convert vacancy‐dopedp‐HgCdTe, is found to induce exactly the same changes inn‐HgCdTe as obtained by ion milling. Since these two, rather different, processes both produce very deep type conversion in vacancy‐dopedp‐HgCdTe, and also produce identical long‐range electrical changes inn‐HgCdTe, it is concluded that both processes share the same damage mechanism which includes the production and diffusion of interstitial mercury.

ISSN:1071-1023    

DOI:10.1116/1.586272

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

A technique for studying low concentrations of trap levels in narrow‐gap Hg1−xCdxTe has been combined with the deliberate introduction of defects to determine the activation energies of these impurities in this ternary material. In this investigation, mercury (Hg) interstitials, believed to be responsible for dark current in metal‐insulator‐semiconductor devices, were deliberately introduced into samples withx≊0.22 andx≊0.24. Each sample was divided into two parts with the second part of each slice used as a control. The results from these samples provide direct evidence that Hg interstitials create trap levels near 45 and 60 meV above the valence‐band edge for thesex‐value samples.

ISSN:1071-1023    

DOI:10.1116/1.586273

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

Defects are a well‐known source of problems in lowxHg1−xCdxTe and Hg1−xZnxTe. To gain insight into the relative importance of various native point defects in these materials we have calculated the formation energy of native point defects in HgTe using a full‐potential linearized muffin‐tin orbital method. This method employs no shape approximation to the energy functional and permits the prediction of the lattice relaxations from first principles. In the present work, only breathing‐mode relaxations were included. Formation entropies resulting from the change to the phonon spectrum upon formation of a defect were calculated using a valence force field model for the elastic contributions and a rigid ion model for the Coulomb contributions to the dynamical matrix. The energies and entropies were incorporated into mass‐action equations to deduce the relative defect concentration. In agreement with experiments, we find mercury vacancies are the dominant defect to accommodate excess tellurium in the lattice when the material is equilibrated in the presence of mercury vapor; we predict that tellurium antisites are dominant in material equilibrated with tellurium solid. Of the defects that accommodate excess mercury, we find that mercury antisites may be more prevalent than previously thought. Extensions to the alloy are also discussed.

ISSN:1071-1023    

DOI:10.1116/1.586274

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

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.

ISSN:1071-1023    

DOI:10.1116/1.586275

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

A new intrinsic defect, the mercurous ion (Hg–Hg)2+, is proposed to account forn‐type doping of Hg1−xCdxTe by excess mercury. The double cations can be formed through capture of neutral interstitial mercury atoms by mercuric ions. This effectively decouples the mercuric ion from the four tellurium atoms previously coordinated, releasing two electrons for each mercury atom captured. This model can explain the stability of metal‐rich MCT and recent reports of intrinsic acceptor–donor pairs correlated within a lattice constant. Formation of mercurous ions could greatly enhance self‐diffusion of Hg through a knock‐on effect. Thermodynamic calculations support the proposition that self‐compensation of indium in MCT can occur through the presence of nearly equal populations of In3+(donor) and In+(acceptor), as occurs in the stable phase InTe. For low or metastable doping levels, the solid phase can be considered as a solid solution of InTe, In2Te3, and MCT. Any excess trivalent In is perfectly compensated by introduction of a cation vacancy for every two In3+ions. On subsequent mercury‐rich annealing, only the excess In3+will be ‘‘activated’’ through filling of cation vacancies, imposing a limit to the maximumn‐type doping achievable.

ISSN:1071-1023    

DOI:10.1116/1.586276

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

Long‐wavelength infrared molecular‐beam epitaxial (MBE) HgCdTe films with dislocation densities as low as 2.3 × 105cm−2on (211) GaAs and Si substrates have been obtained by postgrowth thermal annealing and thermal cycle annealing processes (300–490 °C). Experiments show that metalorganic chemical vapor deposition (MOCVD) HgCdTe epilayers require a higher thermal annealing temperature than MBE material and the difference in dislocation reduction between MBE and MOCVD HgCdTe materials is caused by dislocation movement under high‐temperature and thermal stress conditions. The CdTe buffer layer has been observed to play a significant role for the dislocation reduction in the HgCdTe epilayer grown on GaAs or Si alternative substrates. To study the role of dislocations on MBE HgCdTe/GaAs, systematic measurements of the minority carrier lifetime of MBE HgCdTe grown on both CdZnTe and GaAs substrates were carried out. A strong correlation between minority carrier lifetime and dislocation density is observed.

ISSN:1071-1023    

DOI:10.1116/1.586277

出版商:American Vacuum Society    

年代:1992

数据来源: AIP