It is shown that strained isoelectronically doped buffer layers grown on GaAs and InP wafers allow one to reduce the dislocation density drastically by a factor greater than 20. Correspondingly, the photoluminescence efficiency of near-band-edge emission is enhanced by about the same factor. By deep level transient spectroscopy measurements practically no deep levels can be detected in contrast to uncoated wafers. Applied to device fabrication a great improvement is found in comparison to conventionally fabricated optoelectronic and electronic devices.

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We measure the spectrum of radiative emission from a high quality HEMT device and relate this to the energy distribution of the channel electrons The discussion focuses on the intraband and interband contributions to the spectrum. The intraband. bremsstrahlung component gives evidence for very energetic electrons ( T e , sz 6000 K). The radiative recombination of carriers, however, is characterized by a very much lower temperature.

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