InP-based multiple quantum well structures grown with tertiarybutylarsine (TBA) and tertiarybutylphosphine (TBP): Effects of growth interruptions on structural and optical properties

In this paper, we investigate the effect of interfacial layers on GalnAs(P)/GalnAsP and GalnAs/InP multiple quantum well structures with x-ray diffraction and photoluminescence. We observe a decrease in the room temperature and low temperature photoluminescence intensity as the number of periods is increased which we attribute to the interfaces. Furthermore, different growth interruption schemes show that decomposed As species from TBA have an effect on the structural and optical quality of these structures at both the lower and upper interfaces due to As carry-over. The effect of this carry-over is shown in structural measurements and laser diode results.     

HgCdTe/CdZnTe P-I-N high-energy photon detectors

Classical solid-state detection of x-ray and gamma-ray radiation consists of a high voltage applied between two metallic contacts sandwiching a high resistivity, high dielectric strength material; high voltage and high resistivity are required to enable complete charge collection while minimizing the resolution-degrading leakage current (dark current). We report here the conception and successful fabrication and test of a new device construct which changes this paradigm. P-type and n-type layers are fabricated by mercury cadmium telluride (HC.T) liquid phase epitaxy (LPE) on opposite sides of a high-quality wafer of CdZnTe (CZT) in order to construct a p-i-n diode structure. Wafers up to 9 cm² area have been grown. This diode structure provides an extremely high effective resistivity and barrier to the flow of dark current in the device. Several wafer lots have repeatably yielded p-i-n detectors which exhibit typical diode current-voltage (I-V) curves with very low dark currents at very high bias voltages. Spectra obtained from these detectors produce exceptionally sharp photopeaks which exhibit very little low-energy tailing.     

Interface strain in InGaAs-InP superlattices

Strain has been measured within (001) oriented OMVPE grown multilayer superlattices consisting of thin As-compound layers in InP and thin P-compound layers in GaAs. From the strain behavior, it is interpreted that As rapidly replaces P on an InP surface exposed to AsH₃ and P slowly replaces As on a As-terminated surface exposed to PH₃. This results in incorporation of an InAs-like strain in InP whose magnitude depends on the nature of the As-terminated surface. At growth temperatures above 600°C, the strain is equivalent to about one monolayer of InAs; while below 600°C, it is equivalent to two monolayers of InAs. PH₃ interaction with GaAs surfaces is sufficiently slow that GaP-like strain is observed only when deliberate interrupts under PH₃ are introduced. GaP grown on GaAs at 650°C is found to incorporate enough residual As to sustain a layer composition of GaAs_0.5P_0.5 over the first several monolayers.     

Passivation of Hg1-xCdxTe by photochemical native oxidation: Quantitative analysis of oxide composition

The composition of photochemically grown native oxides on Hg_1-xCd_xTe (x = 0.3) has been analyzed and depth profiled using x-ray photoelectron spectroscopy and Rutherford backscattering spectroscopy. The oxide films were grown in either N₂O or O₂ ambients, and differences in the oxidation process were examined by varying the time and temperature of oxide growth. Under all growth conditions, oxides grown in an O₂ ambient exhibited a higher Hg concentration in the bulk oxide region when compared to N₂O grown oxides. The Hg/Te ratio of all the oxides was found to be less than the starting Hg_1-xCd_xTe substrates and, in some cases, this may be leading to an accumulation of Hg in the oxide/Hg_1-xCd_xTe interface region. For growths at higher temperatures (∼75°C), the excess Hg was seen to move from the oxide/Hg_1-xCd_xTe interface region to the oxide surface. In O₂ ambients, the Hg accumulated at the surface of the oxide whereas for growths in N₂O, it was lost to the ambient. Previous results on photochemical oxidation of Hg_1-xCd_xTe show an inverse relationship between oxide growth rate and temperature. Evidence obtained in this study from oxide compositions, depth profiles and annealing at higher temperatures, suggest that this relationship between oxide growth rate and temperature is primarily due to temperature induced differences in the oxidizing ambient, and not the result of a change in the film growth mechanism due to changing diffusion characteristics with temperature.     

Mercury interstitial generation in ion implanted mercury cadmium telluride

Junction formation and stability in ion implanted mercury cadmium telluride critically depend on the ability to generate Hg interstitials. The creation of Hg interstitials is found to strongly depend on the preferred lattice position of the element implanted. Elements that substitute onto the cation sublattice create significantly more Hg interstitials than elements that sit interstitially or on the anion sublattice. Recoils from implant damage also contribute to Hg interstitial formation in heavier mass implants (Z ≥ of mass Zn), but appear to have negligible influence on interstitial generation in implants of lighter ions. The combination of implanting ions of large mass and high solubility on the cation sublattice produces strong Hg interstitial sources. Implants with these ions can form deep junctions even in heavily doped substrates. Junction stability is also improved with the stronger interstitial source.     

High temperature stability of chromium boride ohmic contacts to p-type 6H-SiC

Ohmic contacts have been fabricated on p-type 6H-SiC using CrB₂. Two hundred nanometer thick films were sputter-deposited on substrates of doping concentration 1.3×10¹⁹ cm⁻³ in a system with a base pressure of 3×10⁻⁷ Torr. Specific contact resistances were measured using the linear transmission line method, and the physical properties of the contacts were examined using Rutherford backscattering spectrometry, x-ray photoelectron spectroscopy, and transmission electron microscopy. The as-deposited CrB₂ contacts exhibited rectifying characteristics and contained oxygen as a major contaminant. Ohmic behavior with linear current-voltage characteristics was observed following short anneals at 1100°C for 2 min at a pressure of 5×10⁻⁷ Torr. The oxygen in the CrB₂ films was removed by the annealing process, and the lowest value of the specific contact resistance (r_c) measured at room temperature was 8.2×10⁻⁵ Ω-cm². Longer anneals at 1100°C for 3.5 h and 1200°C for 2 h reduced the room temperature values of r to 1.4×10⁻⁵ Ω-cm². A thin reaction region has been identified at the CrB₂/SiC interface; however, the interface remains essentially stable. Thermal stressing at 300°C in vacuum for over 2200 h produced only a slight increase in the specific contact resistance. The low value of the specific contact resistance and the excellent high temperature stability of the CrB₂/SiC interface make this contact a candidate for high power/high temperature SiC device applications.     

Crystallographic texture of C54 titanium disilicide as a function of deep submicron structure geometry

Detailed analysis of the crystallographic texture of C54 TiSi₂ was performed and showed a strong correlation between the geometry of the silicide structures and preferential crystallographic orientation. The study was undertaken on blanket and patterned TiSi₂ films formed in the reaction between 32 nm of Ti and undoped polycrystalline silicon using both in situ x-ray diffraction during heating and post-anneal four-circle pole figure reflection geometry measurements. Full pole figures were taken to determine the distribution of C54 TiSi₂ grain orientations in narrow (0.2 to 1.1 μm) lines which was compared with similar results obtained from unpatterned (blanket) films. While in blanket films we found the presence of weak <311> C54 TiSi₂ crystallographic orientation perpendicular to the sample surface, the <040> preferential orientation dominated in patterned submicron line structures and increased with decreasing linewidth. Using pole figure analysis, we observed strong <040> fiber texture in narrow lines with a slight variation in the tilt of the (040) planes normal in the direction perpendicular to the line (full width at half maximum [FWHM] ≈6°), but very little along the length of the line (FWHM ≈2°). In addition, a preferred in-plane (azimuthal) orientation of <040> crystals was found which showed that most of the <040> grains had their (004) plane normals oriented parallel with the line direction. These findings support a model of the C49 to C54 TiSi₂ transformation involving rapid growth of certain orientations favored by the one-dimensional geometry imposed by narrow lines.     

Comparison of X-ray diffraction methods for determination of the critical layer thickness for dislocation multiplication

We present a comparison of x-ray diffraction methods for the determination of the critical layer thickness for dislocation multiplication in mismatched heteroepitaxy. The conventional x-ray diffraction method for determination of the critical layer thickness is based on the direct observation of the lattice relaxation in measurements of strain (the “strain method”). An indirect method is based on the observation of the x-ray rocking curve broadening by the threading dislocations, which are introduced concurrently with misfit dislocations (the “full width at half maximum (FWHM) method”). For this study, we have applied both methods to ZnSe grown on GaAs (001) by metalorganic vapor phase epitaxy (MOVPE). We have compared the resolution of the two x-ray diffraction methods both theoretically and experimentally for the case of 004 reflections using Cukα₁ radiation. Theoretically, we have shown that in this case the FWHM method is 2.6 times more sensitive to relaxation than the strain method. This conclusion is supported by our experiments, in which we determined a critical layer thickness value of 140 nm by the FWHM method, compared to 210 nm as determined by the strain method.     

X-ray lithography,where it is now,and where it is going

This paper describes the x-ray lithography (XRL) systems presently developed, including the present state of source, resist, mask technology, and exposure tools. Future directions in mask substrate materials, and alternative x-ray sources will be presented.     

深亚微米同步辐射x射线光刻技术

报道了我们制作深亚微米 x射线掩模的工艺和同步辐射 x射线曝光工艺 ,并报道了我们在北京同步辐射装置 (BSRF) 3B1 A光刻束线所获得的深亚微米 x射线光刻图形的实验结果