A GaAs/GaAlAs/GaAs/GaAlAs heterostructure has been prepared on a GaAs susbtrate, bonded to 7056 Corning glass, and the substrate and first AlGaAs removed chemically, utilizing the differential etching characteristics of GaAs and AlGaAs in NH4OH−H2O2 and HF solutions. The resulting structure of GaAs/AlGaAs/glass has excellent layer morphology, uniform thickness, and good transmission photocathode performance.

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The ternary-phase diagram of GaAsSb has been calculated using Darken's quadratic formalism for a ternary liquid and assuming a regular solid solution. Liquid epitaxial layers of GaAsxSb1−x have been grown in the range 0.75>x>1 on {100} and {111} GaAs substrates. Results are in excellent agreement with the calculated phase diagram. Variation of bandgap with composition of the layer has been determined by transmission, photoemission, and x-ray fluorescence experiments. The data were fitted to a curve of the form EG=A+Bx+Cx2, where A=0.725 eV, B=−0.32 eV, and C=1.02 eV. Graded bandgap layers have been obtained, with gradients of 700 eV/cm near the substrate interface and 25 eV/cm for thick layers. For use as high-efficiency photoemitters, the samples were doped p type by the addition of elemental Zn to the melt. Cesium and oxygen surface layers were used to lower the work function. Quantum yields of 0.1%–0.2% at 1.06 μ were obtained. Field assisted photoemission in a graded bandgap sample has been calculated and demonstrated experimentally.

Calculations show that very nearly bulk quality material is required for high-efficiency semitransparent III-V photocathodes. For narrow-band response, this can be obtained by epitaxially growing a thin layer of a semiconductor whose bandgap is slightly less than that of the substrate. Cathodes made by growing GaAsSb on GaAs have given quantum efficiencies comparable with front surface values, peaking out at 0.54% at 1.35 eV near the onset of absorption in the GaAs substrate. Preliminary results demonstrating semitransparent yield at 1.06 μ of 0.013% are also shown.

normalIn×normalGa1−×normalAs layers grown by liquid‐phase epitaxy were obtained in the range of 0.0<×<0.23 , when grown on the (111 Ga) plane of GaAs. Attempts to grow alloys on the (110), (111 As), (100), and (112 As) planes resulted in polycrystalline layers. The alloy composition was determined by x‐ray fluorescence and the band gap by infrared transmission. The ternary‐phase diagram was calculated using Darken's quadratic formalism to describe the ternary liquid and assuming the solid solution in equilibrium with the liquid to be regular. It was found that the experimental results were in good agreement with the calculated phase diagrams. A number of liquidus isotherms were calculated in the temperature range of 700°–1200°C. Gallium arsenide isoconcentration curves are shown for 0.95, 0.90, 0.80, 0.50, and 0.30 normalGaAs mole fraction.