Degradation Mechanism of AlGaAs/InGaAs Power Pseudomorphic High-Electron-Mobility Transistors under Large-Signal Operation

Abstract

We have comprehensively investigated the degradation mechanism of output power in AlGaAs/InGaAs pseudomorphic highelectron-mobility transistors (PHEMTs) under large-signal operation. The degradation of output power is caused by the decrease in maximum drain current (I max ) around the knee voltage (V k ) with an increase in drain resistance (R d ). The decrease in I max originates from a degradation layer containing a significant amount of oxygen formed at the drain recess surface region. This layer causes a reduced carrier density in the drain region underneath, resulting in a decreased I max and an increased R d . The decrease in I max is accelerated with increasing drain voltage, temperature, and humidity. These results suggest that the degradation of output power in the PHEMTs is mainly determined by the growth of a corrosion layer owing to an electrochemical reaction between O 2 and/or H 2 O and the semiconductor surface. We successfully suppress the output power degradation due to this electrochemical corrosion reaction with the help of a special surface treatment prior to the deposition of a passivation film on the recess surface. We demonstrate a highly reliable RF operation of PHEMTs in air even without a hermetic package.

Corrosion-induced degradation of GaAs PHEMTs under operation in high humidity conditions

“…Previous results that I max change increased by RH 3 and exp (V gd ) [6] agrees well with eq. (2) and eq.…”

“…2. From these results, we proposed the mechanism of degradation under humidity, bias and temperature [6]. I max reduction is caused by the surface degradation attributed to a corrosion reaction of semiconductor surface with oxygen or H 2 O enhanced by electric field.…”

“…These experimental results of the degradation rate can be explained by a proposed mechanism that the degradation is caused by surface electrochemical corrosion reaction taking place at the drain surface between semiconductor and H 2 O. It was found that the degradation rate is changed by RH 3 , exp (V gd ), and exp (-E a /kT a ), where E a is activation energy and k is Boltzmann constant [6]. According to the electrochemical corrosion reaction model, we showed theoretically that V gd lowers E a .…”

“…We have previously reported a comprehensive study of the dependence of degradation in PHEMTs on bias (V gd ), ambient temperature (T a ), and relative humidity (RH) [6][7]. These experimental results of the degradation rate can be explained by a proposed mechanism that the degradation is caused by surface electrochemical corrosion reaction taking place at the drain surface between semiconductor and H 2 O.…”

Improvement of yield ratio of ohmic contact to GaAs/AlGaAs heterostructure by application of SiO2 protective layer

“…A SiO 2 protective layer has been employed to improve the yield ratio of the contact resistance by preventing the corrosion of GaAs observed along the edge of a photoresist. The mechanism of corrosion of GaAs and the technique for reducing corrosion have been reported [3,4], and the effectiveness of a protective layer that extends the QHR device lifetime has also been reported [5]. In this paper, we report the use of SiO 2 as a protective layer to improve the yield ratio of the contact resistance.…”