AlGaN photodetectors for the UV‐C spectral region on planar and epitaxial laterally overgrown AlN/sapphire templates

Abstract

We present Schottky type metal semiconductor metal (MSM) AlGaN photodetectors (PDs) suited for the ultraviolet C (UV‐C) spectral region grown on conventional planar AlN templates in comparison with epitaxial laterally overgrown (ELO) AlN templates. On planar templates solar blind MSM PDs with state‐of‐the‐art dark current in the pA range and a power independent responsivity are obtained. Using ELO templates with sapphire substrates tilted to the m direction the defect density in the absorber material is reduced compared to that for planar templates. The MSM PDs on this ELO templates exhibit photoconductive gain leading to external quantum efficiencies of up to 77 at 30 V applied bias surpassing that of the planar grown PDs by a factor of 100. In spite of the high gain these PDs also show low dark currents in the pA range up to 100 V applied bias, short switching times and two operating regimes with power independent responsivity. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Defect analysis in AlGaN layers on AlN templates obtained by epitaxial lateral overgrowth

“…In comparison, the coalescence of ELO-AlN(m) templates can be easily controlled. Their successful use as templates for LEDs operating in the UV-B wavelength region as well as solar-blind AlGaN based UV photodetectors has been already demonstrated [3,7,8].…”

“…As result, ELO-AlN layers with a threading dislocation density in the range of 10 8 cm À 2 have been demonstrated in recent work [5,6]. These thick layers can be used as templates for deposition of AlGaN-based optoelectronic devices [3,7,8]. In this case the ELO-AlN templates have to be overgrown by Al x Ga 1 À x N buffer layers with different Al contents x.…”

“…1), ELO-AlN(m) layers of about 7 mm in thickness are currently used as templates for subsequent deposition of AlGaN-based heterostructures for optoelectronic applications [3,7,8]. The reason for this change is a higher wafer curvature observed for the 12 mm thick ELO-AlN(m) layers at room temperature, which causes problems during the subsequent wafer processing.…”

“…According to this analysis the lateral defect distribution is strongly inhomogeneous with a higher density above the ridges and a lower density in the wing regions. The inhomogeneous dislocation distribution in ELO-AlN(m) results in a strong anisotropy of optical and electric characteristics of the AlGaN layers grown on ELO-AlN(m) templates [7,8].…”

“…Thus, in the present study we have analyzed defect reduction mechanisms in the ELO-AlN templates as well as defect behavior in ternary Al x Ga 1 À x N layers grown on these templates. In addition we have summarized the previously published results [9,[12][13][14] in order to compare comprehensively the structure of thick ELO-AlN templates overgrown by AlGaN layers, which are suitable for subsequent growth of LED heterostructures [3] as well as AlGaN-based photodetectors [7,8].…”