Electrical degradation of InAlAs/InGaAs metamorphic high-electron mobility transistors

Abstract

InAlAs/InGaAs metamorphic High Electron Mobility Transistors (HEMT) hold promise for power-millimeter wave applications. A major reliability concern in some of these devices is the degradation of the drain resistance that is observed when the device is electrically stressed for a long time at bias conditions necessary for power applications. The goal of this thesis was to find the physical origin of this reliability problem and to suggest solutions to it. State-of-the-art InAlAs/InGaAs metamorphic HEMTs, provided by our sponsor, Hewlett Packard, were stressed under different bias schemes. It was found that most figures of merit associated with the drain-side of the device degrade under severe bias stress. In particular, the drain resistance, RD, has been found to increase significantly. In order to understand the physical origin of this degradation, we have studied the degradation of simpler Transmission Line Model (TLM) structures. We have found that in TLMs and HEMTs there appear to be two different degradation modes, both associated with hot electrons. In the first degradation mechanisms, we postulate that hot electrons are trapped by defects at the interface between the GaAs etch-stopper and the AlInAs Schottky barrier layer, depleting the carrier concentration in the channel underneath. In the second mechanism hot electrons degrade the InGaAs ohmic contacts. No degradation mechanism associated with the metamorphic nature of the structure has been identified. AcknowledgementsI would like to thank Prof. Jesus del Alamo for giving me the chance to work on this interesting project. He has guided me through this research with a huge amount of patience, ideas and red ink, teaching me a methodology in research and reporting. He always tried to make time available for me, even if he was extremely busy. I would like to thank him for offering me the opportunity to be a teaching assistant for his very interesting class and for giving me a place at MIT from the time I arrived. This research has been funded by Hewlett-Packard. I would like to thank Don D'Avanzo for starting this project, appropriating the funding and giving me the opportunity to work as a SEED student in Santa Rosa. Larry Studebaker, thanks for the invaluable help and the samples during the year and the supervision this Summer. I am very happy that I have found such a great co-advisor. I had a great time in Santa Rosa and I learned a lot there, also thanks to Dan Scherrer, Fred Sughiwo and Bob Yeats. HP Labs also helped me a lot through this thesis. Hans Rohdin, thank you for answering so many questions, reading this thesis on time and sending me the samples that helped pull things together. Thanks to Arlene Wakita and Nick Moll for making these devices available to me.Roxann Blanchard, thanks for all the discussions we held and the questions you answered, even when you were busy with your own thesis. You have proven to be an infinite well of knowledge and I can only hope I have been able to soak up enough of it to continue this research.Tassan...

Degradation Uniformity of RF-Power GaAs PHEMTs Under Electrical Stress

“…To accelerate degradation and, thus, maximize productivity, an aggressive bias current (close to I max and nearly triple the typical operating current) was used. In addition, V DS was stepped-up in regular intervals [13]. During stressing, I D and I G were measured.…”