Indium–silicon co-doping of high-aluminum-content AlGaN for solar blind photodetectors

Abstract

We report on an indium–silicon co-doping approach for high-Al-content AlGaN layers. Using this approach, very smooth crack-free n-type AlGaN films as thick as 0.5 μm with Al mole fraction up to 40% were grown over sapphire substrates. The maximum electron concentration in the layers, as determined by Hall measurements, was as high as 8×1017 cm−3 and the Hall mobility was up to 40 cm2/Vs. We used this doping technique to demonstrate solar-blind transparent Schottky barrier photodetectors with the cut-off wavelength of 278 nm.

Ohmic Contact to High-Aluminum-Content AlGaN Epilayers

“…These act as acceptors and compensate the free electron concentration, thereby reducing the electrical conduction. 3,4 Due to these mechanisms, the n-type doping efficiency is much lower in high-aluminumcontent AlGaN epilayers as compared with in GaN, and hence it is very difficult to make high-current-carrying linear ohmic contacts to such AlGaN epilayers.…”

“…As the aluminum percentage is increased to more than 40%, oxygen atoms tend to occupy DX centers and act as a deep-level defect. 3,4 Their activation energy increases and hence the carrier concentration in the high-Al-content AlGaN layers decreases.…”

Solar-blind AlGaN-based Schottky photodiodes with low noise and high detectivity

“…The reported best detector performances obtained with solar-blind AlGaN Schottky photodiodes include a maximum responsivity of 0.07 A/W at 290 nm along with a NEP of 6.6ϫ10 Ϫ9 W, 18 a minimum c of 278 nm and a minimum dark current density of 6.6ϫ10 Ϫ6 A/cm 2 . 19 In this letter, we demonstrate low noise solar-blind AlGaN-based Schottky photodiodes with very low dark current and high detectivity.…”

“…2 Moreover, its intrinsic solar blindness ͑for x у0.38) and the ability of operation under harsh conditions ͑high-temperature and high power levels͒ due to its wide band gap makes Al x Ga 1Ϫx N-based photodetectors attractive for high-performance solar-blind detection applications. Several research groups have demonstrated successful solarblind operation with Al x Ga 1Ϫx N photodetectors using photoconductive, 3,4 p -i -n, [5][6][7][8][9][10][11][12][13][14] metal-semiconductormetal ͑MSM͒, 15,16 and Schottky [17][18][19][20] detector structures. Cutoff wavelengths ( c ) as short as ϳ225 nm, an ultraviolet/ visible rejection over 5 orders of magnitude along with responsivities as high as 0.12 A/W at 232 nm were reported using a Al 0.7 Ga 0.3 N p -i -n detector structure.…”

Ultraviolet light-emitting diodes at 340 nm using quaternary AlInGaN multiple quantum wells

“…Both of these layers were n doped to 1ϫ10 18 cm Ϫ3 using an In/Si codoping approach. 15 The device active layers consisted of a quaternary Al 0. 15 In 0.02 Ga 0.83 N/Al 0.1 In 0.01 Ga 0.89 N MQW, the barrier and well layer thickness of which were each kept at 15 Å and the number of wells was varied from 0 to 10.…”