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INTRODUCTIONNucleation and subsequent material characteristics of CdTe-epitaxial layers on high-Miller-index Si surfaces are of interest from a crystallographic point of view. Additionally, understanding the nature and quality of epitaxy on different Si surfaces is important because composite substrates [Cd(Zn)Te/ZnTe/Si], if produced with high crystal perfection, can be used to fabricate HgCdTe-based, large-format, infrared focalplane arrays. To this end, a decade of research has been conducted on the growth of Cd(Zn)Te(112)/ Si(112) because this is currently the preferred orientation for HgCdTe grown by molecular-beam epitaxy (MBE). However, only minimal work has been done to fully understand the nucleation process of II-VI compounds on nonpassivated and arsenic-passivated Si(112) and other high-Miller-index surfaces. Results from these initial studies indicate that Te 2 exposure of arsenic-passivated Si(112)-nominal substrates leads to a Te surface coverage of 20-30%. 1,2 From this information, a step-flow growth model was developed for CdZnTe growth on Si(112)-nominal substrates.Several groups have also reported on the MBE growth of Cd(Zn)Te on Si (112) substrates misoriented toward the [111] direction; however, only a few studies address the MBE-growth process on Si(112) substrates misoriented away from the [111] direction or on even higher Miller-index surfaces, such as Si(113). 3-6 Material properties from these studies vary greatly depending on the precise nucleation and growth method used. Also indicated is that the CdTe-epilayer orientation does not necessarily reproduce the Si-substrate orientation. However, no model was presented that would explain the change in epilayer orientation. Therefore, to address these issues, a systematic investigation on nucleation properties as well as an investigation on the overall epilayer-material properties as a function of Si orientation was undertaken. The family of Si{111}-type surfaces that are off-cut from {111} in the range of 0-30°were studied. Specifically, passivation, nucleation, and epitaxial growth on Si(111), Si(112) tilted 5°toward [111], Si(112) nominal, Si(112) tilted 5°away from [111], and Si(113) substrates were investigated. A detailed study of the atomic configuration of these and other Si surfaces has been reported. 7 Figure 1 shows the ideal, nonprimitive surface structures of Si(112) and Si (113) Tellurium-adsorption studies were conducted on {111}-type Si surfaces that are off-cut from the {111} in the range of 0-30°on both nonpassivated-and arsenicpassivated Si surfaces. Relative surface coverages as a function of Te exposure time and Si-surface orientation were obtained with in-situ x-ray photoelectron spectroscopy (XPS). The XPS results indicate that Te coverage on arsenicpassivated Si surfaces increases as the step density of the surface increases. In contrast, Te-adsorption studies conducted on nonpassivated-Si surfaces showed no dependence between Te coverage and the surface-step density. Subsequent ZnTe and CdTe molecular-beam epitaxial ...

The type III band alignment of HgTe/CdTe superlattices leads to the interesting possibility of achieving very long wavelength infrared (VLWIR) (15 µm and longer) cutoff wavelengths with either normal (HgTe layer thickness less than about 70 Å for CdTe layer thickness of 50 Å) or inverted (HgTe thickness greater than about 70 Å) band structures. The inverted band structure superlattices promise even greater cutoff wavelength control than the normal band structure ones. However, the electronic band gaps of inverted band structure superlattices are substantially less than their optical band gaps, leading to large thermal carrier concentrations even at temperature as low as 40 K. These high carrier concentrations in turn give rise to more rapid Auger recombination than normal band structure superlattices with the same cutoff wavelengths. We conclude that the highest performance is expected from VLWIR HgTe/CdTe superlattice-based detectors with normal band structure absorber layers.

X-ray photoelectron spectroscopy (XPS) was used to study the clean surface of ZrB2 (0001). The clean surface exhibits Zr 3d5/2 and Zr 3d3/2 peaks at 179.2 and 181.6 eV, respectively. However, angle resolved XPS indicated ZrO2 peaks at 183.5 and 185.7 eV at higher emission angles, indicating that further cleaning was necessary. After additional cleaning cycles, these oxide peaks were no longer observed at high emission angles. This result demonstrates the necessity to probe the near surface region with higher emission angles on very reactive surfaces, in order to completely establish the cleanliness of the surface.

We report here molecular beam epitaxy (MBE) mercury cadmium telluride (HgCdTe) layers grown on polished and repolished substrates that showed state-of-the-art optical, structural, and electrical characteristics. Many polishing machines currently available do not take into account the soft semiconductor materials, CdZnTe (CZT) being one. Therefore, a polishing jig was custom designed and engineered to take in account certain physical parameters (pressure, substrate rotational frequency, drip rate of solution onto the polishing pad, and polishing pad rotational velocity). The control over these parameters increased the quality, uniformity, and the reproducibility of each polish. EPIR also investigated several bromine containing solutions used for polishing CZT. The concentration of bromine, as well as the mechanical parameters, was varied in order to determine the optimal conditions for polishing CZT.