Growth and properties of semi-insulating epitaxial GaAs

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Abstract
We have found that in order to grow liquid-phase epitaxial (LPE) semi-insulating gallium–arsenide layers, chromium must be used to form deep energy levels, and the shallow donors and acceptors must be self-compensated. The shallow and deep levels appear to be dependent on impurities that arise from chemical reactions between the growth system components. The reactions can be controlled by systematic bakeouts of the arsenic-saturated gallium melt before each growth. This effect has been dramatically demonstrated in layers grown from melts baked out in the temperature range from 600 ° to 850 °C. For example, layers grown from melts baked out below and above ∠775 °C in a fused quartz–graphite–hydrogen growth system change from an n- to p-type, respectively. The bakeout transition temperature is essentially independent of the growth temperature and the Cr concentration. The resistivity in layers grown from undoped melts increases smoothly through the transition range. However, the resistivity reaches a peak of ∠300 Ω-cm in layers grown from Cr-doped melts baked out at the transition temperature. Electrical and mass spectrographic measurements on layers grown from undoped and Cr-doped melts indicate that electrical and chemical compensation occurs between impurities in the melt and in the layer. Photoluminescence measurements at 77 °K show 1.3 and 0.8 eV emission bands for n- and p-type layers grown from Cr-doped melts, respectively. In the high-resistivity layers, many unidentified deep levels are observed from 0.6 to 1.2 eV that parallel levels found in a Cr-doped, semi-insulating GaAs substrate.

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