Leak current in high resistive GaN buffer layer and its light responsiveness

Abstract

We observed unique light responsiveness in HR GaN leak current, in which the current was drastically reduced under LED illumination of 2.65 eV or lower photon energy. Free carrier excitation by the illumination and consequential electron capture into the electron traps would rationalize the phenomenon. The threshold energy in our measurement was well associated with the carbon related very deep electron trap reported elsewhere (P. B. Klein et al., Appl. Phys. Lett. 79, 3527 (2001) [3]). Observation of this phenomenon provides us a very simple way to characterize both the HR GaN resistivity and the concentration of electron traps in the GaN buffer simultaneously.1 Introduction GaN based high electron mobility transistor (GaN HEMT) has attracted significant attention in the compound semiconductor industry because of its supreme high power handling capability in microwave applications, especially for wireless mobile base stations [1]. Regarding the field effect transistor operations, high resistive (HR) GaN buffer layer plays an important role in the epitaxial layer structures because its quality would severely affect the breakdown voltage, pinch-off performance, isolation of the devices, and other DC and RF characteristics. The controversial current collapse or electron trap phenomenon in GaN HEMT [2], which is usually recognized as a surface state problem, has also been associated with the quality of underlying HR GaN buffer layers [3]. Achieving consistency between the high resistivity and low current collapse in HR GaN buffer layer would be therefore, one of the most important technical breakthroughs which realize prime GaN HEMT device performances. Thus the authors concentrated on characteristics of the HR GaN buffer layers, which were grown at varying process conditions, and found a unique relationship between the leak current and the photon energy of the illuminated light during the measurement. In this paper, the "odd" I-V characteristics of the leak current were described and then a model to rationalize this phenomenon will be proposed. The model would provide a very simple characterization method which quantitatively measures the current leakage and the degree of electron traps in HR GaN buffer layers simultaneously. The possible causes of the phenomenon will also be mentioned.

Roles of lightly doped carbon in the drift layers of vertical n-GaN Schottky diode structures on freestanding GaN substrates

“…19) Since a nitrogen-site carbon is known to act as an acceptor under certain conditions, 20,21) carbon likely plays a major role in governing the above-mentioned nonlinear behavior accompanying Si doping. [22][23][24][25] It should also be noted that free-carrier concentration affects the balance between breakdown voltage and series resistance in the vertical diodes: A low free-carrier concentration deteriorates series resistance. In contrast, a high free-carrier concentration deteriorates breakdown voltage.…”