Two-photon depth sectioning of GaN

Traditionally, the absorption depth of UV excitation in GaN (typically 50-100 nm) has limited PL studies to near-surface material. By combining two-photon excitation, Confocal Scanning Optical Microscopy (CSOM), and Solid Immersion Microscopy (SIM), we now optically section through GaN with a depth resolution of less than 2 μm. This enables us to optically study GaN surfaces, bulk, and interfaces that up to this point were accessible only by physically altering the sample (for example, by cleaving, etching, or sputtering away material). In this talk, data on impurity concentrations as a function of depth will be specifically discussed.