We demonstrate high-performance ultraviolet photodetectors (UV-PDs) based on lattice-matched (LM) InAlN/AlGaN heterostructure field-effect transistors (HFETs) gated by transparent ITO films. Low dark currents of 6.8 × 10−8 and 6.1 × 10−7 A/mm and high photocurrent gains over four and three orders of magnitude were obtained for the LM In0.12Al0.88N/Al0.21Ga0.79N and In0.10Al0.90N/Al0.34Ga0.66N HFETs, respectively. The negative threshold voltage shifts under illumination indicate that most of the photo-generated carriers are transported in the two-dimensional gas (2DEG) region around the InAlN/AlGaN interface. High peak responsivities of 2.2 × 104 and 5.4 × 104 A/W and large UV-to-visible rejection ratios greater than 104 and 103 were achieved for the LM In0.12Al0.88N/Al0.21Ga0.79N and In0.10Al0.90N/Al0.34Ga0.66N HFET-type UV-PDs, respectively. These improved performances with respect to other AlGaN UV-PDs around the same wavelength detection range may possibly be attributed to the greater contribution of the photogenerated electrons to the 2DEG, which results from the increase in the polarization sheet charge density at the InAlN/AlGaN interface. The LM InAlN/AlGaN heterostructures provide relatively promising candidates for realizing high-performance HFET-type UV-PDs.
In order to improve the thermal stability in AlGaN-channel two-dimensional electron gas (2DEG) heterostructures, we newly designed straincontrolled quaternary AlGaInN barrier layers, and then we grew them by metalorganic chemical vapor deposition. A 2DEG density as high as 2.5 × 10 13 cm −2 and a good surface morphology were obtained for an (Al 0.64 Ga 0.36 ) 0.976 In 0.024 N/Al 0.19 Ga 0.81 N heterostructure, in which in-plane tensile strain in the barrier layer was estimated to be 0.51%. It was also confirmed that the (Al 0.64 Ga 0.36 ) 0.976 In 0.024 N/Al 0.19 Ga 0.81 N heterostructure showed an excellent thermal stability in its 2DEG properties even at high temperatures up to 900 °C. As a result of their thermal stability improvement, we were also able to confirm that the contact resistance was improved by applying high-temperature annealing.
In this study, Al2O3-gate-insulated metal-insulator-semiconductor (MIS) heterostructure field-effect transistors (HFETs) were fabricated using an Al0.61Ga0.37In0.02N/Al0.18Ga0.82N two-dimensional-electron-gas heterostructure, and their electrical properties were characterized. It was confirmed that the thermally stable quaternary AlGaInN barrier layer contributed to a good ohmic contact resistance of 10.5 Ω mm. This value seemed to be considerably small as an AlGaN-channel heterostructure. The fabricated MIS-HFETs showed good pinch-off characteristics and exhibited a maximum drain current (IDSmax) of approximately 180 mA/mm at the gate bias of +2 V. A high off-state breakdown voltage of 2.5 kV was obtained for the device with a gate-to-drain length of 20 μm.
An InAlN/AlGaN two-dimensional electron gas (2DEG) heterostructure with an "regrown AlN initial layer" was grown on AlN/sapphire template by metalorganic chemical vapor deposition, and their structural and electrical properties were investigated. It was confirmed that the prepared sample had an atomically-smooth heterointerface and exhibited an improved 2DEG mobility of 242 cm 2 /Vs compared to the sample without the regrown AlN layer.
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