Deep ultraviolet photodetectors grown by gas source molecular beam epitaxy on sapphire and AlGaN/sapphire substrates

摘要

Optically-based chemical and biological sensors require optoelectronic devices with specific emission and detection wavelength ranges. Semiconductor optoelectronic devices applicable to this sensing are of particular interest due to their low power consumption, compact size, long lifetime, and low cost. We report the electrical and optical properties of deep UV p-i-n photodiodes (PDs) based on short period superlattices (SPSLs) of AlN/AlGaN. All device and test structures are grown by gas source molecular beam epitaxy with ammonia on sapphire and AlGaN/sapphire substrates. AlGaN/sapphire substrates were grown by stress controlled hydride vapor phase epitaxy (HVPE). The cutoff wavelength of PDs based on these SPSLs can be varied from 250 to 280 nm by changing the SPSL barrier/well thickness ratio. For mesa diodes with 150 μm diameter we obtain extremely low dark leakage current of ～3 pA/cm~2, and high zero-bias resistance of ～6 x 10~(14) Ω. A cutoff wavelength of 247 nm is obtained for these devices with four orders of magnitude rejection by 315 nm. We obtain a maximum responsivity of 60 mA/W.