ＧａＡｓを用いたサブミリ波天文学用光伝導検出器の開発 ＧａＡｓの超高純度液相エピタキシャル成長

Liquid phase epitaxial (LPE) growth from Hg-rich solution is investigated in the case of HgTe-based quaternary semiconductors Hg1−x−yCdxZnyTe and Hg1−x−yCdxMnyTe and the ternary Hg1−xCdxTe. In contrast to the results for Hg1−xCdxTe, the LPE growth can give crystals of quaternary alloys with excellent compositional uniformity. The uniform compositional profiles of the epilayers are revealed by electron probe microanalysis, both in the plane and along the growth direction. The growth of Hg1−xCdxTe by the same LPE method yields a large compositional gradient along the growth direction. Thus we have clearly demonstrated that homogeneity of epilayers are improved by incorporation of Zn or Mn during the crystal growth. A typical sample of as-grown Hg1−x−yCdxZnyTe, with x=0.17 and y=0.10 (Eg≊320 meV at 77 K), showed n-type conduction with a carrier concentration of 1×1016 cm−3 and a mobility of 9×102 cm2/V s at 77 K. As-grown Hg1−x−yCdxMnyTe showed n-type conduction with a carrier concentration of 3×1014 cm−3 and a mobility of 8×104 cm2/V s at 77 K for a typical sample with x=0.16 and y=0.009 (Eg≊150 meV at 77 K).

We have used the liquid phase epitaxy (LPE) and vapor phase transport epitaxy (VPTE) growth methods to fabricate double heterojunction (DH) CaTe/HgCaTe/CaZnTe and heterojunction CaTe/HgCaTe thin film materials. The detector of zero tunnel leakage current has been developed successfully by using these materials. The advantages of the VPTE method are as follows: (1) There is increased stability of surface of detector; (2) bulk band-to-band tunnel effect in detector will not occur and trap- assisted tunnel effect will be reduced owing to the N+-p junction and IR absorption region of the detector separated by using this DH material; (3) Ro is enhanced at the same time, so that sensing circuit of FPA can attain much higher injection efficiency; (4) we overcome mother solution of the Te-rich back melt HgCaTe by LPE growth CaTe on HgCaTe/CaZnTe, and (5) this growth method hardly changes characteristics of HcCgTe.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Fabrication of YBCO thick films on Nd 2CuO 4 buffered Ni tapes by liquid phase epitaxy

Beam lead GaP electroluminescent diodes have been developed using a quasi-planar configuration. This new structure couples the advantages of beam lead technology to the high-efficiency GaP p-n junctions prepared by liquid phase epitaxial (LPE) growth. The devices consist of a p-type (Zn, O-doped) LPE mesa formed on an n-type (Te-doped) LPE layer grown on an n-type Czochralski-grown substrate. A deposited insulator film covers the entire mesa surface and passivates the exposed junction perimeter. Ohmic contacts are made to both the p- and n-regions through holes in the insulating layer and beam leads are applied by conventional technology. The finished devices are shaped into domed structures during the final separation of the wafer into individual devices. Complete devices bonded to substrates were operated at 10 mA with typical forward voltages of 1.95 ± 0.05 V with external quantum efficiencies of 2-2.25 per cent (unencapsulated). This beam lead quasi-planar structure takes advantage of the inherently large size of the individual devices dictated by optical considerations and allows a number of improvements in device design. The areas where advantages over existing GaP diodes can be realized are as follows, 1) Optimization of external efficiency by contact design and diode configuration is possible. 2) Planar beam lead processing and junction passivation methods can be used, 3) Array fabrication in discrete or monolithic forms is feasible.

The possibility of using liquid phase epitaxy (LPE) to grow GaAsxSb1−x on InP substrates has been investigated. Theoretical phase-diagram calculations for the GaAsSb system show the solidus compositions in the x?0.5 region, where lattice matching to InP occurs, to be strongly dependent on temperature and in some cases multivalued, making it extremely difficult to achieve the degree of temperature control required for deposition of uniform LPE layers. When growths were attempted two-phase deposits were consistently found, an observation which supports the above conclusions. Appreciable rapid dissolution of the InP substrates was also observed. It is concluded that successful LPE growth of GaAsSb lattice-matched to InP is unlikely by conventional variable-temperature LPE techniques.

Y-system coated conductor on metal substrate by LPE method

Surface morphology, electrical and optical properties of gallium antimonide layers grown by liquid phase epitaxy

The vapor–liquid–solid (VLS) growth mode is expected to achieve high-quality REBa2Cu3Oy thin films at a high growth rate since it is almost identical to the liquid phase epitaxy (LPE) growth mode. We studied the effect of the deposition rate on superconductivity in SmBa2Cu3Oy (Sm123) thin films prepared using the VLS growth mode. The VLS-Sm123 films as well as that deposited by pulsed laser deposition (PLD) under optimal conditions had completely c-axis orientation and maintained high crystallinity. Critical temperatures were around 90 K and independent of the deposition rate. However, critical current densities increased with the deposition rate and reached over 1 MA/cm2 at 77 K. In this study, a maximum deposition rate of 320 nm/min was achieved; this was thirty times as high as that obtained by PLD. We propose that a deposition rate as high as that obtained by LPE can be achieved by the VLS growth mode.

This paper reports the deposition of (100) GaAs and (111)B CdZnTe layers on silicon substrates up to 4-inch diameter to produce substrates suitable for liquid phase epitaxy (LPE) of high-quality HgCdTe layers. Metalorganic chemical vapor deposition is used for both GaAs and CdZnTe in a reactor capable of deposition onto eighteen 3-inch or ten 4-inch wafers per run. An encapsulation scheme is described that prevents contamination of a Te melt by Si or GaAs during LPE growth. Excellent uniformity of thickness and Zn concentration are achieved in the MOCVD films. The CdZnTe films show only lamellar twins close to the GaAs interface; no twins capable of propagating into the HgCdTe layer are formed. These substrates have been used for the growth of pure HgCdTe films having a dislocation density that is only a factor of 2 to 4 higher than that measured in similar films grown on bulk CdTe substrates.

The chemistry and composition of grain boundaries in polycrystalline GaAs grown by liquid phase epitaxy (LPE) and molecular beam epitaxy (MBE) are examined using complementary Auger electron spectroscopy (AES), secondary ion mass spectroscopy (SIMS) and x-ray photoelectron spectroscopy (XPS). The effects of an unintentional residual-oxygen partial pressure during LPE growth are investigated in terms of grain boundary passivation. Depth-compositional data verify the grain boundary localization of oxides using an in situ, UHV fracturing technique. Indications of distributions of these oxides over the grain boundary are presented. The performances of Au Schottky barrier solar cells fabricated from the polycrystalline LPE and MBE GaAs are compared and differences are explained in terms of grain boundary activity.

Periodic doping and heterostructure multilayers of Ga xIn 1− xAs yP 1− y: LPE growth and characterization

We have investigated the in-plane homogeneity of the large LPE (liquid phase epitaxy) crystals in microstructure and the growth mode in order to clarify the growth mechanism. The growth rate distribution dependence on the crystal rotation was observed in 20×20 mm2 LPE films. In the YBa2Cu3O7−δ system the higher rotation rate caused a larger growth rate distribution. It was considered that the distribution of both the growth interface temperature and the solute diffusion boundary layer thickness was existed. In this paper, we have focused the effect of the heat flux from the bottom of the crucible (hot region) during the LPE growth. Investigation of the growth rate distribution in the NdBa2Cu3OX(NdBCO) system was effective in order to confirm the influence of the heat flux, since the influence was negligible for the LPE growth in the NdBCO system. The higher rotation rate in the NdBCO system caused a smaller growth rate distribution. These phenomena could be explained by the difference in the crystal rotation effect on the growth interface temperature.

The influence of Yb added to the melt, on the near-band-gap emission of Ga1−xAlxAs grown by liquid phase epitaxy, is reported. No characteristic Yb3+ emission is found, but a pronounced narrowing of the bound-exciton spectrum is observed for Yb concentrations in the Ga melt below 100 ppm. A similar effect is seen in conduction band to acceptor transitions, for which the smallest linewidth observed is limited by fluctuations in composition and agrees well with the currently accepted 66:34 band-offset partition between the conduction and valence bands of GaAs/Ga1−xAlxAs heterojunctions in the direct band-gap range.

Liquid phase epitaxy growth and structural characterization of highly-doped Er3+:LiYF4 thin films

Superconducting YBa2Cu3Oy films were grown by liquid-phase epitaxy (LPE) on NdGaO3(l10) single-crystalline substrate by a modified top-seeded crystal growth method. Two different melt compositions were used. In the case of Cu-poor melt composition (Ba:Cu=3.0:5.0), only c-axis oriented growth was observed. However, if we used Cu-rich melt composition (Ba:Cu=3.0:6.5), both c-axis and a-axis oriented films were obtained. In the latter case the crystalline orientation of YBa2Cu3Oy films was dependent on the temperature of the surface of the melt. At lower temperatures, c-axis orientation films were obtained, whereas the films showed a-axis orientation at higher temperatures. The width of transition temperature range of orientation is very narrow, less than 3 °C, compared to the width observed in the conventional vapor phase depositions (which is typically 50 °C). We propose that orientation change in the liquid phase epitaxial growth is determined by the unique properties of the phase diagram of Y-Ba-Cu-O-system.