Microscopic Defects in Semi‐Insulating GaAs and Their Effect on the FET Device Performance

Abstract

Epitaxial layers were grown on semi‐insulating LEC substrates by the chloride CVD technique and depletion type MESFET's with a gate length of 0.5 ̈m have been fabricated on these epitaxial layers. Correlation between the FET device performance and the substrate quality has been studied. It was found that the substrate quality largely affects the device performance. Dislocations of the substrate had no definite effect on the device performance, while the density of the precipitate‐like microscopic defects revealed by AB solution had a decisive effect on the device performance and the uniformity. We have examined LEC substrates with various density of etch pits revealed by AB solution (AB‐EPD) but with nearly the same order of dislocation density revealed by etching. The AB‐EPD ranged from less than 104 to, while the average dislocation density was in the range of . The standard deviation of the compression over 2 in. ∅ wafers was very small in the case of low AB‐EPD wafers, while it was very large in the case of high AB‐EPD wafers. When the substrate with FETs was etched by AB solution after the device performance measurement, it became evident that FETs with several AB etch pits under the gate area exhibited lower performance. It was also found that the photoluminescence intensity and its distribution over the substrate corresponded with the etch pit pattern generated by the AB solution.