We present optical characterizations on three AlxGa1-xN/GaN high electron mobility transistor (HEMT) structures with different Al compositions using photoluminescence (PL), contactless electroreflectance (CER), photoreflectance (PR), photoconductivity (PC) and persistent photoconductivity (PPC) measurements. The samples used in this study were grown by metal organic chemical vapor deposition (MOCVD) on sapphire substrates, and were designated as samples A (x=0.07), B (x=0.11), and C (x=0.13). From PL and PR spectra the interband luminescences of GaN and AlxGa1-xN are identified, and hence the Al composition x can be determined. From CER spectra, we found a broad feature related to 2-dimensional electron gas (2DEG) and AlxGa1-xN bandgap transition with Franz-Keldysh oscillations (FKOs) in the high-energy end. The Al composition x is confirmed from the bandgap energy of AlxGa1-xN layer deduced from CER spectra, and the built-in electric field in the barrier layer can be determined by analyzing the period of FKOs. It has been shown that the internal electric field in AlxGa1-xN layer is enhanced as the Al composition is increased. For sample C, the PC and PPC spectra excited by different monochromatic lights have been done at room temperature and different decay times were evaluated.
|Number of pages||3|
|Journal||Physica E: Low-Dimensional Systems and Nanostructures|
|Publication status||Published - 2008 Mar 1|
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Atomic and Molecular Physics, and Optics
- Condensed Matter Physics