The Effects of P 2 S 5 Surface Passivation on Dry Etched GaAs
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THE EFFECTS OF P2S. SURFACE PASSIVATION ON DRY ETCHED GaAs O.J. Glembocki*, J.A. Dagata", E.A. Dobisz" and D.S. Katzer" * Naval Research Laboratory, Code 6864, Washington, DC 20375 ** National Institute of Standards and Technology, Gaithersburg, MD 20899.
ABSTRACT The effects of P 2S, surface passivation treatments on damage caused by chemically assisted ion beam (CAIBE) etching of GaAs have been examined using ex-situ photoreflectance. Epitaxially grown undoped GaAs on heavily doped GaAs substrates were used to determine surface electric fields. The etching process is observed to decrease surface electric fields, produce subsurface damage and to reduce surface photovoltages. Post-etching treatments with P 2S5 are observed to increase surface photovoltages, but have no significant effect on the surface fields or subsurface damage. That the surface field is unaffected suggests that in etched materials the Fermi level pinning is not solely determined by the surface and that the near surface regions are important. We also find that samples pretreated with P2 5, exhibit more etch damage than those which are only degreased.
INTRODUCTION Dry etching techniques such as chemically assisted ion beam etching (CAIBE), reactive ion etching and plasma etching are widely used in the formation of two and three dimensional microstructures and nanostructures. Because these etching techniques involve energetic ions, some level of electrical damage is unavoidable, even in the case of etched surfaces, which are very smooth and exhibit physical roughness only on a nanometer scale. This type of electrical damage can take the form of surface and bulk charge traps, which can deplete carriers from electronic devices[l] and decrease photoluminescence efficiencies in optical devices. The trap densities associated with this type of damage are typically between 10 15 cm"3 and 10 cm'3 .[1,2] Recently, Dagata and coworkers[3] have developed a new surface passivation technique for GaAs, involving UV-ozone oxide growth followed by a chemical etch and finally passivation with P2S5. This treatment produces a thin, uniform oxide, which is resistant to further oxidation. In scanning tunneling microscope images, GaAs samples treated in this manner have exhibited improved ambient tunneling properties. These results suggest that the P 2S5 treatment may have a beneficial effect on electronic properties of GaAs surfaces and thus it may be possible to use this treatment to improve dry etched surfaces. In this paper, we have examined the possibility of using P2 55 surface passivation treatments to control and modify the etch damage introduced during CAIBE etching of GaAs. We have used photoreflectance to study the surface photovoltage, surface potential and subsurface damage in epitaxial undoped GaAs layers (UN) grown by molecular beam epitaxy (MBE) on n÷ GaAs substrates.[4] Because of the high quality of the epitaxial layers, these samples have been shown to exhibit strong Franz-Keldysh effects, which can be used to accurately determine the surface electr
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