Determination of bandgap states in p-type In[subscript 0.49]Ga[subscript 0.51]P grown on SiGe/Si and GaAs by deep level optical spectroscopy and deep level transient spectroscopy

Abstract

The presence and properties of traps in p-type In[subscript 0.49]Ga[subscript 0.51]P grown on low dislocation density, metamorphic Ge/SiGe/Si substrates and GaAs substrates were determined using deep level transient spectroscopy (DLTS) and deep level optical spectroscopy (DLOS) leading to the quantification of trap behavior throughout the entire 1.9 eV bandgap of the In[subscript 0.49]Ga[subscript 0.51]P material as a function of substrate. Thermal emission-based DLTS revealed a single hole trap at E[subscript v] + 0.71 eV for growth on both lattice matched and mismatched substrates with similar concentrations. Complementary, optical emission-based DLOS measurements detected bandgap states at E[subscript v] + 1.18 eV, E[subscript v] + 1.36 eV, and E[subscript v] + 1.78 eV for p-type In[subscript 0.49]Ga[subscript 0.51]P grown on both substrate types. The total concentration of the DLOS-detected states was found to comprise approximately 80% of the entire trap concentration in p-type In[subscript 0.49]Ga[subscript 0.51]P bandgap. This relatively high concentration of above midgap levels may be of great significance for minority carrier devices that utilize p-type In[subscript 0.49]Ga[subscript 0.51]P (such as high efficiency III–V multijunction solar cells) since their position in the bandgap and high concentrations suggest that strong minority carrier electron trapping behavior can be expected. The primary effect of substituting the GaAs substrate by Ge/SiGe/Si is to increase the concentration of these states by a factor of 2–3, with no additional levels detected due to the replacement by the Si-based substrates, indicating that all detected traps are native to the epitaxial In[subscript 0.49]Ga[subscript 0.51]P material (regardless of the substrate), but whose concentrations appear to be influenced by dislocation density.