Optical anisotropy and spontaneous ordering inGa0.5In0.5P: An investigation using reflectance-difference spectroscopy

We have applied reflectance-difference spectroscopy (RDS) to the study of optical anisotropy in spontaneously ordered Ga[sub 0.5]In[sub 0.5]P grown by metal-organic chemical-vapor deposition. The degree of order in Ga[sub 0.5]In[sub 0.5]P has been associated previously with a shift of the band-gap energy [Delta][ital E][sub 0] and a crystal-field valence-band splitting [Delta][sub [ital C]]. Theoretically, both quantities are, to first order, quadratic functions of the long-range order parameter [eta], which varies from 0 to 1 for disordered and perfectly ordered Ga[sub 0.5]In[sub 0.5]P, respectively. The main RD spectral feature in partially ordered Ga[sub 0.5]In[sub 0.5]P is a bulk-induced, asymmetric peak at [ital E][sub 0] with a long tail that extends well below [ital E][sub 0] and a sharp high-energy cutoff at [ital E][sub 0]+[Delta][sub [ital C]]. We find experimentally and theoretically that the intensity of this RD spectral feature is proportional to [radical]([Delta][ital E][sub 0]) and, therefore, is linear with the order parameter. This makes RDS particularly useful for measuring the optical anisotropy of high-band-gap Ga[sub 0.5]In[sub 0.5]P. We also compare heterostructures of GaAs and Al[sub 0.5]In[sub 0.5]P on Ga[sub 0.5]In[sub 0.5]P with uncoated Ga[sub 0.5]In[sub 0.5]P in an effort to separate bulk-, surface-, and interface-induced RD spectral features.