Mechanisms for output power expansion and degradation of PHEMT's during high-efficiency operation

• Published in: IEEE transactions on electron devices Vol. 46; no. 8; pp. 1608 - 1613
• Main Authors: Leoni, R.E., Hwang, J.C.M.
• Format: Journal Article
• Language: English
• Published: IEEE 01-08-1999
• Subjects: Breakdown; Buffers; Degradation; Devices; Drains; MESFETs; MODFETs; Simulation; Stresses
• ISSN: 0018-9383; 1557-9646
• DOI: 10.1109/16.777147

PHEMT stability in high efficiency power amplifiers (where the PHEMT is typically driven into reverse gate-drain breakdown) has been examined under accelerated dc stresses. Such stresses initially caused a slight increase in drain current and decrease in threshold voltage due to hot-carrier injection into the buffer which was not seen in similarly stressed MESFET's. On the other hand, continued stressing resulted in significant decrease in drain current and increase in drain resistance due to hot-carrier injection into the surface passivation which is consistent with the typical MESFET degradation mode. The degradation rate of PHEMT's is approximately two orders of magnitude faster than that of MESFET's. Two-dimensional physical device simulation confirms that the faster degradation of PHEMT's is due to their higher sensitivity to surface conditions.