Pressure dependence of optical transitions in In0.15Ga0.85N/GaN multiple quantum wells

The effects of hydrostatic pressure on optical transitions in In0.15Ga0.85N/GaN multiple quantum wells (MQW close-quote s) have been studied. The optical transition associated with confined electron and hole states in the MQW close-quote s was found to shift linearly to higher energy with pressure but exhibit a significantly weaker pressure dependence compared to bulklike thick epitaxial-layer samples. Similar pressure coefficients obtained by both photomodulation and photoluminescence measurements rule out the possibility of the transition involving localized states deep in the band gap. We found that the difference in the compressibility of InxGa1-xN and GaN induces a tensile strain in the compressively strained InxGa1-xN well layers, partially compensating the externally applied hydrostatic pressure. This mechanical effect is primarily responsible for the smaller pressure dependence of the optical transitions in the InxGa1-xN/GaN MQW close-quote s. In addition, the pressure-dependent measurements allow us to identify a spectral feature observed at an energy below the GaN band gap. We conclude that this feature is due to transitions from ionized Mg acceptor states to the conduction band in the p-type GaN cladding layer rather than a confined transition in the MQW close-quote s. copyright 1998 The American Physical Society