Low-Frequency Noise Characterization in AlGaN/GaN HEMTs with Varying Gate Recess Depths
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Low-Frequency Noise Characterization in AlGaN/GaN HEMTs with Varying Gate Recess Depths Shrawan. K. Jha1a, Bun. H. Leung1, Charles C. Surya1, Heins Schweizer2, and Manfred. H. Pilkhuhn2b 1 Department of Electronic Engineering, The Hong Kong Polytechnic University, Hong Kong. 2 Department of Physics, University of Stuttgart, Germany. a email: [email protected] b Present address: National Chiao Tung University, Taiwan, R.O.C. ABSTRACT Low-frequency noise measurements were performed on a number of AlGaN/GaN HEMTs with different gate recess depths, which were formed by dry etching. Detailed characterizations of the low-frequency noise properties were performed on the devices as a function of as a function of hot-electron stressing conducted at VD = 10 V and VG = -1.5 V. The room temperature voltage noise power spectral density, SV(f), of the devices were found to show 1/f dependence. A comparison of SV(f) measured from different devices clearly indicate increase in the noise levels for the devices with large recess depths, reflecting the degradation caused by ion-impact induced damage during recess formation. Furthermore, the results of low-frequency noise measurements showed fast degradations for the devices with larger gate recess depths. Our experimental data clearly show that the dry etching process has induced damages in gates. INTRODUCTION Gallium nitride (GaN) is a direct, wide band-gap semiconductor with high saturation velocity and breakdown field making it a material of choice for high-temperature microwave power amplifiers [1,2]. Recent development of flip-chip integrated circuit amplifiers and monolithic distributed amplifiers using GaN-based HEMT technology clearly demonstrates the superior properties of the devices [3-7]. The performance of the GaN HEMTs can be improved at high frequency applications by employing the gate-recessing technique, which enhances the transconductance of the devices and also reduces the source resistance. Reactive ion etching and chemical etching are the possible processes to create recessed gate structure [8,9]. Typically reactive ion etching technique is commonly employed for the formation of gate recesses of the order of several nanometers. The process utilizes energetic ions and that may cause physical damages to the material in the recessed region strongly affecting the integrity and the lifetime of the devices. In this paper we present systematic investigation of the effects of gate recess etching, using reactive ion etching technique, on the electronic properties of the HEMTs. Low-frequency excess noise study presented here is an important aspect in this paper as the noise is an important figureof-merit particularly when the devices are used for signal amplification [10,11]. In addition, since the low-frequency excess noise is directly proportional to the trap density at the AlGaN/GaN interface it can be utilized as an effective tool for monitoring the degradation in the integrity of the AlGaN/GaN interface due to high voltage stress applied on the devices. T
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