摘要:

In this article we report on a new type of spectroscopy for impurity and/or defect levels in the energy gap of narrow‐gap semiconductors using the near‐band‐gap photon energies from a laser. This spectroscopy is done under the conditions of intense laser photoexcitation and is associated with the Auger relaxation processes of hot electrons involving impact ionization of valence electrons into impurity or defect levels. Wavelength‐independent structure in the photoconductive response versus magnetic field is observed at high intensities in samples of Hg1−xCdxTe withx≊0.22 and 0.24. This structure arises from hot electrons photoexcited high into the conduction band by sequential absorption of CO2laser radiation. The hot electrons lose their energy by impact ionizing valence electrons into impurity/defect levels in the gap. For the sample withx≊0.22 and an energy gap of 95 meV, three levels are found at 15, 45, and 59 meV above the valence band. A level at 61 meV is found for the sample withx≊0.24 and a gap of 122 meV.

ISSN:0734-211X    

DOI:10.1116/1.585810

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

The dislocation density variations in HgCdTe films grown by liquid phase epitaxy (LPE) from tellurium‐rich melts were measured and were found to depend on film growth temperature, substrate dislocation density, epitaxial film thickness, and postgrowth annealing in Hg vapor. Thin films, less than about 30–40 μm in thickness, exhibit dislocation densities which generally follow the dislocation densities of the substrates. In thicker epitaxial films, however, dislocation multiplication can accompany Te precipitation and subsequent low temperature annealing in Hg vapor, thereby, raising the density of dislocations by as much as a factor of 3–10. Use of a high temperature preanneal in Hg vapor can be employed to eliminate dislocation multiplication during low temperature annealing. When this preanneal is used in conjunction with very thick film growth with thicknesses greater than about 80 μm, dislocation densities in the LPE films can fall to values below those in the substrate. The dependence of metal–insulator–semiconductor storage times on dislocation densities in these films has also been measured.

ISSN:0734-211X    

DOI:10.1116/1.585811

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

We present results for the surface binding energies for HgTe and CdTe that will serve as input for molecular beam epitaxy growth models. We have found that the surface binding energies are surface orientation dependent and are not simply proportional to the number of first‐neighbor bonds being made to the underlying layer. Moreover, because of the possibility of charge transfer between cation and anion surface states, one may have large differences between the binding energy for the first and the last atom in a given layer, and these differences will be different for the narrow‐gap, less ionic materials than for the wide‐gap, ionic materials. We also find that the surface states associated with an isolated surface atom or vacancy are extended in materials with small gaps and small effective masses, and thus call into question the modeling of surface binding by simple pair interactions.

ISSN:0734-211X    

DOI:10.1116/1.585812

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

HgCdTe epilayers and lattice matched CdZnTe (111) substrates have been investigated by x‐ray photoelectron diffraction to characterize their surface structure in regard to termination, reconstruction and relaxation as well as in regard to degradations. Well‐ordered CdZnTe surfaces of stoichiometric composition were realized by Ar ion sputtering, while sputter cleaning of the HgCdTe epilayers led to a significant increase of the CdTe mole fraction in the surface region. However, the crystallinity of the HgCdTe surfaces is found to be maintained in spite of their compositional degradation. Ordered and nondegraded HgCdTe(111) surfaces are obtained by electrochemical etching. The examined (111)A and (111)B surfaces can be easily differentiated since their photoelectron diffraction patterns indicates a surprisingly perfect termination. Evidence for any reconstruction or relaxation of the investigated (111) surfaces of CdZnTe and HgCdTe is not found.

ISSN:0734-211X    

DOI:10.1116/1.585813

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

The surface polarity of a mercury cadmium telluride (MCT) (111) crystal surface has been determined by x‐ray photoelectron diffraction (XPD). Emission from the core levels of Hg, Cd, and Te gave reproducible photoelectron diffraction patterns with considerable fine structure. Comparisons between experiment and single scattering cluster calculations viaRfactors very well distinguished the different kinds of lattice sites of Cd, Hg, and Te, and also permitted unambiguously assigning a cationic termination to the sample studied. This is thus a demonstration of the capability of XPD to study the type of termination involved at MCT and other compound semiconductor surfaces.

ISSN:0734-211X    

DOI:10.1116/1.585814

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

A novel electrochemical approach based on voltammetric studies of reactions occurring at the HgCdTe/electrolyte interface has been devised to clean and reconstruct the HgCdTe surface prior to passivation. Sequential potential steps, applied to a HgCdTe specimen immersed in an electrolyte, oxidize the surface, remove Hg and leave a thin protective CdTe layer, reconstructed from the lattice atoms. A thick CdTe dielectric can be subsequently electrodeposited on this surface. The electrochemically processed interfaces were characterized by a low (1010cm−2 V−1) density of fast interface states, negligible concentration of slow traps and unusual stability to prolonged air exposure and to 100 °C air anneal. The electrochemical technique was further developed as a surface characterization tool to assess the quality of Br2‐etched HgCdTe surfaces. Monolayers of Te remaining on Br2‐etched surfaces convert sequentially to TeO2and then to HgTeO3on air exposure.

ISSN:0734-211X    

DOI:10.1116/1.585374

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Fluoridic films produced by the anodization of Hg1−xCdxTe (x∼0.22) surfaces in nonaqueous solutions consist of three distinct regions. A thick uniform region, containing the fluorides of cadmium, mercury, and tellurium, as well as HgTe, is covered by a thin CdF2layer. The third region—the film–substrate interface—poor in mercury, consists mainly of CdF2and TeF4. The anodic film is grown by two mechanisms: the dominant one occurs by motion of the film–substrate interface into the semiconductor, consuming the original surface. There is, however, some growth at the film–electrolyte interface which forms the thin CdF2layer on top of the structure. The CdF2rich region acts as a diffusion barrier for the indiffusion of oxidizing species. Tellurium ions, on the other hand, diffuse to the outer surface to be oxidized there. This diffusion barrier is overcome when the fluorides are thermally stressed in the presence of traces of oxygen, and the film starts to oxidize. However, the film–substrate interface does not degrade unless the film is heavily oxidized. A model for the anodic fluoride structure is presented and discussed in light of the film stability with respect to room temperature post‐growth oxidation and thermal treatments.

ISSN:0734-211X    

DOI:10.1116/1.585375

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Infrared detectors fabricated from Hg1−xCdxTe typically operate in the 60 to 160 K range. The temperature dependence of the atomic structure of HgCdTe may influence device performance. We present the first detailed study of the x‐ray diffraction lattice parameters of molecular‐beam epitaxy grown Hg1−xCdxTe epilayers between 15 and 300 K. The epilayers were grown on (100) oriented CdTe substrates, and varied in thickness (6 to 11‐μm) and composition (x=0–0.172). The (400) reflection was measured to determine the lattice parametera⊥ normal to the film. HgTe (x=0) exhibited normal lattice contraction (α=4.7×10−6±0.3 K−1at 300 K), with a minimum ina⊥ at 60 K, and an expansion ofa⊥ below 60 K. In addition to showing a minimum ina⊥ at 60 K, some of the Hg1−xCdxTe (x≠0) epilayers (10 μm thick) exhibited anomalous behavior with varying degrees of thermal hysteresis ina⊥. The average contraction ofa⊥ for these epilayers from 300 to 60 K is 0.006 Å. This is compared with results we have obtained from a temperature dependent extended x‐ray absorption fine structure study of these HgCdTe epilayers: whereas HgTe exhibited a normal thermal contraction of the Hg–Te bond length consistent with the lattice parameter results, in the HgCdTe epilayers this bond contracts 0.02 to 0.03 Å on cooling from 300 to 10 K. We also present lattice parameter measurements for a thin cap layer of CdTe on HgCdTe. An increase of 0.0134 Å ina⊥ relative to the bulk was observed for a 1000 Å layer of CdTe on HgCdTe at 300 K.

ISSN:0734-211X    

DOI:10.1116/1.585376

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

CdTe, (CD,Zn)Te, and Cd(Te,Se) crystals grown by the Bridgman technique have been characterized by transmission electron microscopy. Results indicate that the Te precipitates are seen in all the crystals, but their density and size are lowest and largest in the case of Cd(Te,Se) crystals. In addition, dislocations, stacking faults, and microtwins are observed in as‐grown CdTe, (Cd,Zn)Te, and Cd(Te,Se) crystals. Arguments have been developed to rationalize these observations and their ramifications on crystal perfection are discussed.

ISSN:0734-211X    

DOI:10.1116/1.585377

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

The composition of high‐quality single‐crystal bulk‐grown Cd1−yZnyTe (0≤y≤0.2) was determined from precision lattice constant measurements for a total of 22 data points. These samples were used to develop calibration curves for an accurate, contactless, nondestructive optical determination of composition using either 300 K transmission measurements or 77 K photoluminescence measurements. The 300 K transmission technique is useful for bulk CdZnTe wafers while the 77 K PL technique is applicable to both bulk and thin‐film CdZnTe. Both techniques are useful in determining Cd1−yZnyTe composition in the range (0≤y≤0.2) which covers the range needed for lattice‐matching to Hg1−xCdxTe and Hg1−xZnxTe epitaxial layers. The ability to map sample composition with high precision is available with both techniques.

ISSN:0734-211X    

DOI:10.1116/1.585378

出版商:American Vacuum Society    

年代:1991

数据来源: AIP