PRESSURE-DEPENDENCE OF OPTICAL-TRANSITIONS IN IN0.15GA0.85N GAN MULTIPLE-QUANTUM WELLS/

The effects of hydrostatic pressure on optical transitions in In0.15Ga 0.85N/GaN multiple quantum wells (MQW's) have been studied. The optica l transition associated with confined electron and hole states in the MQW's was found to shift linearly to higher energy with pressure but e xhibit a significantly weaker pressure dependence compared to bulklike thick epitaxial-layer samples. Similar pressure coefficients obtained by both photomodulation and photoluminescence measurements rule out t he possibility of the transition involving localized states deep in th e band gap. We found that the difference in the compressibility of Inx Ga1-xN and GaN induces a tensile strain in the compressively strained InxGa1-xN well layers, partially compensating the externally applied h ydrostatic pressure. This mechanical effect is primarily responsible f or the smaller pressure dependence of the optical transitions in the I nxGa1-xN/GaN MQW's. In addition, the pressure-dependent measurements a llow us to identify a spectral feature observed at an energy below the GaN band gap. We conclude that this feature is due to transitions fro m ionized Mg acceptor states to the conduction band in the p-type GaN cladding layer rather than a confined transition in the MQW's. [S0163- 1829(98)51940-6].