Influence of disorder on the optical absorption in semiconductors: Application to epitaxially grown III-V compounds

The influence of disorder on optical properties of semiconductors is discussed in different models: phenomenological model of partially relaxed $\mathbf{k}$-selection rule, spectral density model, and the model taking into account excitonic effects. These models were compared to experimental spectra of disordered GaAs, where disorder was generated either by MBE low temperature growth or by implantation of arsenic. Reasonable agreement between the data and the models was obtained. The analysis of the data supports the view that the main source of disorder in nonstoichiometric GaAs are the defects resulting from the excessive arsenic, e.g., arsenic antisites.

Figure 1

(Color online) Upper row: Experimental absorbance spectra measured at $12\mathrm{K}$ (black) and theoretical curves fitted with RkR model (red) of low temperature GaAs. An arrow at about $1.8\mathrm{eV}$ of LT5 panel marks a possible manifestation of the split-off subband. Lower row: same as above for arsenic implanted GaAs. At about $1.5\mathrm{eV}$ of IM5 panel an emerged excitonic peak is indicated by the arrow.

Figure 2

(Color online) DOS for the Gaussian autocorrelation function with $L=15\mathrm{\AA }$ and $V_{\mathrm{r.m.s.}}$ ranging from $50\text{to}300\mathrm{meV}$. Disorderless square-root DOS is plotted for reference.

Figure 3

(Color online) Absorption for the Gaussian autocorrelation function with $L=15\mathrm{\AA }$ and $V_{\mathrm{r.m.s.}}$ ranging from $50\text{to}300\mathrm{meV}$.

Figure 4

(Color online) Theoretical (solid line) and experimental (dotted line) absorption curves for ion implanted GaAs samples IM4 and IM5. In both cases the correlation length $L=7\mathrm{\AA }$ is assumed while $V_{\mathrm{r.m.s.}}$ is equal to $130\mathrm{meV}$ for IM4 and $100\mathrm{meV}$ for IM5 sample.