Effect of Proton Damage on Optical Modulation Spectra of Gallium Arsenide

Abstract

We studied the effect of proton bombardment on the electroreflectance (ER), electroabsorption (EA), and transmission (T) spectra of high resistivity Cr‐doped single crystal . The high resolution of ER and EA and their sensitivity to crystalline order make it possible to study shift, broadening, and gradual distortion of the spectral peaks as disorder increases with successive irradiations. The sample is bombarded with 150 keV protons. We have measured ER and EA at the absorption edge , ER at the critical point, and d‐c optical absorption. All these measurements are sensitive to proton irradiation of the sample; the most sensitive one is ER at . In the range of , optical absorption just below the energy gap increases sublinearly with proton dose; the peak‐to‐peak amplitudes of ER at and vary linearly with the logarithm of the dose and hence can be used to measure the degree of damage in the sample. The EA signal at develops a tail toward the low energy side of the spectrum. The ER at has a peak shift of ≈4 meV to higher energy while the peak of the ER signal at shifts by about 15 meV to lower energy. Broadening is evident in the ER signals at and . Annealing at 300°C for up to 2 hr only partially recovers the unbombarded state. A model based on the gradual amorphization of the sample by an increasing number of proton damaged, amorphous islands with well‐defined boundaries can partially explain the experimental results.