Abstract
We have studied the effect of molecular-beam epitaxy (MBE) growth conditions on the performance and reliability of npn GaAs–AlGaAs heterojunction bipolar transistors (HBTs). Wafers grown under normal conditions yield devices with high current gain, but suffer premature failure due to interstitial beryllium diffusion from the base into the graded AlGaAs emitter. Wafers grown with high arsenic/gallium flux ratio and reduced substrate temperature during base deposition have high current gain, and are extremely reliable. Mean time to failure, as defined by a 10% reduction in original current gain, is ≳ 108 h at 125 °C junction temperature for devices grown using conditions optimized for device reliability. We believe the ability to produce high reliability HBTs by MBE is vital to future applications of this technology.
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