UV/IR Photodetectors

Group III-nitride materials are superior for advanced UV detector fabrication, due to their wide direct band gap along with high thermal, chemical, mechanical, and radiation tolerance.  Research and development performed by several groups, indicate that effective optical emission and detection can be achieved in a wide spectral band ranging from (200 -1770) nm, which also includes the near IR range. 

The Radio Frequency Molecular Beam Epitaxy (RF MBE) method used in our laboratory for nitride material growth allows fabrication of multilayer structures that incorporate binary, ternary, or even quaternary nitride compounds, with a precise control over the layer, thickness, chemical composition, crystalline quality, and doping during a single-process growth on commercial  sapphire or silicon substrates.

Our preliminary data from GaN, AlGaN, and InGaN based photodiode structures grown on Si and sapphire, indicate that sensitivity in both the UV and IR ranges can be achieved from a single structure.  Measurements performed in our laboratory on GaN/InGaN-based heterostructure chips, show that they can be operated at temperatures over 300 °C without internal or external cooling.

AlN and GaN buffer layers are grown by RF MBE on Si to compensate for the lattice mismatch and reduce the effect of the substrate material on the active AlGaN film grown on the top of the structure.  The content of Al in this film determines the UV cut-off wavelengths of the device and can be varied between 30% and 60%. Spectroscopic ellipsometry is used to determine the band gap of the AlGaN layer. Reflection High Energy Electron Diffraction (RHEED) is used to monitor the crystalline quality of the layers during growth. Post-growth characterization will include photoluminescence (PL), optical transmission, spectroscopic ellipsometry, and Hall Effect measurements.

The current challenge is to take advantage of all the advanced nitride material growth and processing capabilities, as well as the unique optical, chemical, and thermal properties of the nitrides, in order to develop wireless, miniature, inexpensive, and reliable integrated multi-band solar-blind fire detectors.