Charakterisierung und Optimierung von (Al, Ga) N-basierten UV-Photodetektoren (Volume 39) (English shop)

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This work investigated the influences of dislocation density, heterostructure and detector geometry on the electro-optical properties of AlGaN-based metal-semiconductor-metal photodetectors (MSM PD). The focus was on the realisation of Schottky-type MSM PDs that are suitable for photodetection at wavelengths below 300 nm and exhibit the highest possible external quantum efficiency (EQE). Such detectors allow the detection of UV radiation without interference from sunlight.

Based on experimental and simulated data of front- and back-illuminated Al0.5Ga0.5N/AlN MSM PDs on planar sapphire templates, a comprehensive study was compiled in which the threshold and saturation behaviour of the EQE of these devices was attributed to the polarisation charge at the AlGaN/AlN heterojunction. Building on this, the influences of layer structure, electrode geometry and metallisation scheme on the reduction of the required operating voltage were investigated, and these optimisation approaches were combined such that an EQE of 24% at 0 V could be achieved.

In addition, front-illuminated Al0.4Ga0.6N MSM PDs on epitaxially laterally overgrown (ELO) AlN templates were investigated. Thin AlGaN absorber layers exhibited a pronounced inhomogeneity of the material composition. Owing to the associated internal interfaces, photocurrent gain arises, accompanied by increased dark currents. For thick absorber layers, in which the material inhomogeneity is buried deeper below the electrodes, the increase in EQE without gain could be attributed directly to the reduced dislocation density in the AlGaN on the basis of a simple physical model.