Photoreflectance Characterization and Control of Defects in Gan by Etching with an Inductively Coupled Plasma
- PDF / 88,791 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 107 Downloads / 213 Views
L3.56.1
PHOTOREFLECTANCE CHARACTERIZATION AND CONTROL OF DEFECTS IN GaN BY ETCHING WITH AN INDUCTIVELY COUPLED PLASMA O.J. GLEMBOCKI,* D.K. GASKILL,* S.M. PROKES* and S.W. PEARTON,** Naval Research Laboratory, Code 6862, Washington, D.C. , 20375 * Department of Material Science and Engineering, University of Florida, Gainsville, FL 32611
ABSTRACT Photoreflectance (PR) is used to detect and characterize the electronic effects etch-induced defects in GaN that is exposed to an Ar or Ar/Cl inductively coupled plasma (ICP). Because of the sensitivity of PR we can follow the formation of etch-induced defects as a function of ion energies and densities. We show that at low RF powers, below 100W, the surface improves in electronic quality, but as the power is increased beyond 200W, etch-induced defects, are formed. The use of an Ar/Cl mixture plays a critical role in control of etch-induced defects.
INTRODUCTION GaN and its alloys are of great interest because of desirable electronic transport properties inherent to these material systems as well as their good thermal dissipation characteristics. Devices that are made from GaN based materials often involve the formation of recessed gates, which are formed through dry etch removal of material.[1] The etching scheme of choice is inductively coupled plasma etching, which utilizes an inert species such as Ar to provide directional sputtering and a reactive species such as Cl2 to enhance the etch rate and in many cases control the effects of etch-induced damage. A trade-off occurs because the energetic ions can penetrate well below the surface and create defects such as vacancies or interstitials. In GaAs, it was found that a careful balance of ion energy and reactive gas pressure can control the process-induced defects, and in-situ post etch treatments could be used to remove any other residual defects.[2] In the case of GaN, however, such control over defects in processing does not exist, and the only recourse for defect removal is post-etch annealing, which is found to be incomplete. Previous studies of GaN based devices that were exposed to a ICP plasma have shown that the etch damage can have a deleterious effect on device performance.[1] This included reduced Schottky barrier heights as well as motion of the Fermi energy at the surfaces of GaN toward mid gap.[3] These results suggest significant changes to the surface electronic properties of GaN that is exposed to a plasma. In this paper, we take advantage of the fact the photoreflectance spectroscopy (PR) is based on the ability to photomodulate the built-in surface electric field. This ties in directly into the fact that the photomodulation is just a photovoltage. The AC nature of the modulation allows us to explore in a contactless manner the response of the surface states that pin the Fermi-level. Thus changes in the surface potential will directly lead to changes in the PR signal. In addition, the surface photovoltage will also be sensitive to formation of subsurface defects. We show that
L3.56.2
we can follow
Data Loading...
