A novel method to fabricate β-(AlGa)2O3 solar-blind photodetector has been demonstrated. The β-Ga2O3 thin film was first deposited on c-plane sapphire substrate by pulsed laser deposition (PLD) and following by high-temperature annealing (1000°C and above). With a proper annealing condition, the PLD deposited β-Ga2O3 film could be transformed from a binary to become a ternary β-(AlGa)2O3 film, which is resulted from the Al atoms of sapphire substrate diffused into the PLD deposited β-Ga2O3 layer by high-temperature driven, and the Ga atoms from β-Ga2O3 thin film to the substrate diffusion as well. By high-temperature driven interdiffusion method, β-(AlGa)2O3 thin film with designed Al composition and film thickness could be achieved, which could cover higher bandgap larger than 4.9 eV. With such a method, one can achieve β-(AlGa)2O3 Solar-blind photodetector with good crystal quality and surface morphology, which also could push the response wavelength even further to the DUV range.
Polarization-matched quantum wells (QWs) can lead to maximized electron-hole wave functions overlap and low efficiency droop at high current density. By using the modern theory of polarization with hexagonal reference, c-plane InAlN/InGaN QWs were explored and designed for polarization matching. The simulation results show that, even on c-plane, polarization-matched structures can be achieved by adjusting strain and material composition. The In composition of larger than 35% of InAlN was required to match the total polarization of InGaN at any given composition. Considering the bandgap’s bowing factors of III-nitride ternary alloys, In0~0.1Ga1.0-0.9N as quantum barrier (QB) provided enough potential barriers for In0.35~0.45Al0.65-0.55N to form a multiple QW (MQW) structure. The results indicated that improper resistance of MQW and the existing fixed charge between the interfaces of p-type region/MQW and n-type region/MQW could result in nonuniform carrier distributions and current leakage, respectively. Furthermore, we found that In0.41Al0.59N/In0.1Ga0.9N polarization-matched MQW had proper resistance; however, such structure produced a huge polarization fixed-charge between the junction interface. By studying the strain level of InAlN QW and GaN QB, which can be grown on AlN/GaN superlattice templates, the In0.33Al0.67N/GaN polarization-matched MQW structure has been specifically designed with small resistance and without inducing improper polarization fixed charge. By optimizing the number and thickness of QWs, the 425nm LED has relative IQE of 56% and efficiency droop of only 7% at high current density of 333 A/cm2. This study provides guidance for development of In-rich InAlN materials.
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