Extraction of Trap Characteristics from Excess Noise in GaN Devices
- PDF / 66,766 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 81 Downloads / 255 Views
Extraction of Trap Characteristics from Excess Noise in GaN Devices
Alexander A. Balandin Department of Electrical Engineering University of California at Riverside Riverside, California 92521 U.S.A.
ABSTRACT Characteristics of traps are extracted from excess noise spectra of the doped- and undoped-channel GaN/AlGaN heterostructure field-effect transistors. The two types of excess noise that have been analyzed include flicker, e.g. 1/fγ noise, and generationrecombination noise. The average trap density determined for the undoped and doped devices is 1.1 x 1016 cm-3 and 7.1 x 1017 cm-3, respectively. Two distinct trap time constants τ determined for doped devices were 16 µsec and 0.1 msec. The trap characteristics obtained from the analysis of the excess noise spectra are in agreement with data provided by other techniques.
1. INTRODUCTION One of the main obstacles to progress in GaN-based devices has been large trap density in the bulk and surface of the material [1]. The adverse effects of the trap presence in the GaN/AlGaN heterostructure field-effect transistors (HFETs) include transconductance frequency dispersion, current collapse, restricted microwave power, deterioration of 2D carrier confinement, and gate- and drain-lag transients [2]. The traps are also believed to be responsible for relatively high levels of low-frequency excess noise in these devices [3-6]. Investigation of the trap characteristics and their spatial location by different techniques is just at the beginning. The origin of traps is not always known and it is still a question of debate whether the traps are predominately in the interface between the barrier layer and the channel or in the bulk of the barrier layer. Here we present a theoretical analysis of experimental excess noise data with the goal of determining trap concentration and time constants and comparing the values with those obtained by other characterization techniques. The interaction between charge carriers and defects causes low-frequency noise that is referred to as excess noise to distinguish it from intrinsic noise types such as thermal (Johnson) and shot noise. Defects act as capture centers (or traps) each characterized by a different time constant, thus modulating some physical parameter, e.g. the number of free carriers, the mobility, etc., and causing a fluctuation in the electrical quantity under observation.
E5.3.1
2. ANALYSIS OF THE FLICKER NOISE SPECTRA We have analyzed low-frequency noise spectra measured for n-type dopedchannel and undoped-channel AlxGa1-xN/GaN HFETs. The details of the layered structure and measurement procedure have been reported elsewhere [3-5]. The devices with low aluminum content in the barrier (x~15%) have been doped externally in order to achieve in the channel the sheet electron concentration of about ns ~ 1013 cm-2. The devices with high aluminum content in the barrier (x~30%) have not been externally doped, and the same sheet electron concentration ns in these transistors has been achieved via stronger piezoelectric field, whic
Data Loading...
