D Centers in Iii-V Semiconductors Under Hydrostatic Pressure

DX centers are deep level defects found in some III-V semiconductors and their alloys. These defects are characterized by several unusual physical properties, including persistent photoconductivity and a large difference between their thermal and optical ionization energies. We have used hydrostatic pressure as a tool to study the microscopic structure of these defects and examine whether their existence is a general feature of all III-V semiconductors. We have observed a new local vibrational mode (LVM) in hydrostatically stressed, Si-doped GaAs. The corresponding infrared absorption peak is distinct from the Si_{rm Ga} shallow donor LVM peak, which is the only other LVM peak observed in our samples, and is assigned to the Si DX center. Analysis of the relative intensities of the Si DX LVM and the Si shallow donor LVM peaks has been combined with Hall effect and resistivity analysis to infer that the Si DX center is negatively charged. The frequency of this new mode provides important clues to the structure of this defect. We have also discovered a pressure-induced deep donor level in S-doped InP which has the properties of a DX center. The pressure at which the new defect becomes more stable than the shallow donor is 82 kbar. We have measured the optical ionization energy and the energy dependence of the optical absorption cross section for this new defect. We have also determined the capture barrier from the conduction band into the DX state. The fact that DX centers can be formed in InP by applying pressure suggests that the existence of DX states should be very common in n-type III-V semiconductors. We also suggest a method for predicting under what conditions these defects will be the most stable form of the donor impurity.