Photoemission Study of Low-Fluence, Non-Thermal Laser Damage of UHV-Cleaved Gallium Arsenide (110)
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PHOTOEMISSION STUDY OF LOW-FLUENCE, NON-THERMAL LASER DAMAGE OF UHV-CLEAVED GALLIUM ARSENIDE (110) S. S. Goldenberg,' J.P. Long, and M.N. Kabler, Code 4686, Naval Research Laboratory, Washington,
DC
20375-5000
ABSTRACT of The pulsed-laser induced photochemical production metallic Ga islands on the surface of GaAs cleaved, irradiated, is documented through and studied in ultrahigh vacuum (UHV) photoelectron spectroscopy and subsequent scanning electron Ga islands are detected for laser fluences as low microscopy. 2 reported for far below those previously as 1 mJ/cm , modification of GaAs, and for which the temperature rise is negligible.
INTRODUCTION Since the development of injection lasers, it has been known that surfaces of III-V semiconductors can degrade under illumination. More recent experiments have shown that laser irradiation with photons of energies above the band gap and fluences or intensities below melting produces a number effects For example, it has been in surface and near-surface regions. shown that excimer laser irradiation can enhance by more than an order of magnitude the etch rate of GaAs exposed to a chlorine atmosphere (1,2]. On GaAs [3] and GaP (4), pulsed visible-laser induced emission of constituent species has been detected, and reconstructions in the case of GaP, changes in surface lattice Continuous irradiation of have been observed using LEED (5]. GaAs at low intensity causes large decreases in the efficiency of near-band-gap photoluminescence near room temperature (6,7). Raman spectra attributed to solid arsenic have been observed for similarly irradiated GaAs (8]. Several of these experiments have been interpreted as Details of the photofavoring a photochemical mechanism. chemistry remain obscure; almost any reasonable process must involve specific surface or bulk defects, none of which appear yet to have been identified. The present paper describes a different approach to laser We have investigated surfaces cleaved in UHV damage on GaAs. and have applied atom-specific diagnostic techniques using radiation. photoelectron spectra produced with synchrotron These experiments show that, for clean GaAs (110) surfaces a 2.43 eV laser pulses, irradiated with low-fluence, photochemical decomposition of the surface occurs, resulting in sparsely distributed metallic Ga islands separated by regions of Inspection in a scanning electron largely intact surface. microscope (SEM) shows these islands to be roughly hemispherical hundred of diameters up to several with a distribution angstroms.
Mat. Res. Soc. Symp. Proc. Vol. 201.
1991 Materials Research Society
520
EXPERIMENT The experiments were performed at the NRL soft x-ray beam line at the National Synchrotron Light Source. Full instrumental details appear elsewhere [9]. A copper vapor laser was employed, operating at a 6-kHz repetition rate and 510-nm wavelength (an intracavity dichroic mirror removed the 578-nm line). Intracavity optical feedback was introduced (10] which produced linearly polarized pulses with a FWHM of 5 ns. The lase
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