Effect of Photo-Assisted RIE Damage on GaN
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Internet Journal Nitride Semiconductor Research
Effect of Photo-Assisted RIE Damage on GaN Z. Mouffak12, N. Medelci-Djezzar1, C. Boney1, A. Bensaoula1 and L. Trombetta2 1Texas
Center of Superconductivity and Advanced Materials, Department of Physics,University of Houston, of Electrical and Computer Engineering, University of Houston,
2Department
(Received Friday, July 11, 2003; accepted Friday, September 26, 2003)
Reactive Ion Etching (RIE) and Photo-Assisted RIE (PA-RIE) induced damage in GaN using simple Schottky structures and a BCl3/Cl2/N2 gas mixture have been investigated. Schottky diode I-V characteristics following different RF powers and exposure times show significant changes caused by damage. This damage results in a reduction of the reverse breakdown voltage VB in n-type GaN and an increase in VB for p-type GaN. Our preliminary data on the PA-RIE process points to much reduced damage levels compared to conventional RIE. This result may be due to a change in surface chemistry or to a photo-enhanced diffusion of defects into the GaN layer, leaving a cleaner nearsurface region.
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Introduction
There is currently much interest in the development of electronic and opto-electronic devices based on IIINitride semiconductor alloys (principally the binary and ternary alloys of Ga, In, and Al with N). These materials have direct band gaps ranging from 0.7 eV for InN to 6.2 eV for AlN, and high thermal conductivity. Thus they hold promise for a variety of applications that are difficult or impossible to achieve with other materials, including transistors operating at high temperature or high power, and light emitters/detectors in the blue/UV spectrum. [1] [2] [3] In fabricating devices from the III-Nitrides, the use of plasma etching is critical for obtaining anisotropic etch profiles and sufficiently high etch rates. However, plasma techniques induce lattice damage in the semiconductor, resulting in electrically active defects in the near-surface region of the device. Such defects degrade device performance by causing excessive leakage current and reduced optical efficiency, and therefore much effort is expanded to better understand and control the etch process. Studies using inductively coupled plasmas (ICP) show high damage levels that are partially removed by wet etching [4]. While this approach might be adequate for devices fabricated using relatively thick top active layers (i.e. LEDs and some lasers), it is not acceptable in others, where removal of a relatively thick layer after plasma etching may not be possible. This issue will become more acute as device geometries shrink and
sophisticated heterostructures (e.g., the HEMT) become necessary. Furthermore, wet etching is always a potential source of additional surface contamination. Development of an all-dry etching technique that minimizes plasma damage would thus be highly desirable. For this purpose, photo-assisted RIE (PA-RIE) processes have been investigated for a variety of materials [5] [6] [7]. PA-RIE requires minor or no modification to th
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