In0.53Ga0.47As MSM photodiodes withtransparent CTO Schottky contacts and digital superlattice grading |
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Authors: | Wei Gao Berger PR Zydzik GJ O'Bryan HM Sivco DL Cho AY |
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Affiliation: | Dept. of Electr. & Comput. Eng., Delaware Univ., Newark, DE; |
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Abstract: | Metal-semiconductor-metal (MSM) photodiodes with an In0.53 Ga0.47As active region were investigated using a transparent cadmium tin oxide (CTO) layer for the interdigitated electrodes to improve the low responsivity of conventional MSM photodiodes with opaque electrodes. CTO is suitable as a Schottky contact, an optical window and an anti-reflection (AR) coating. The transparent contact prevents shadowing of the active layer by the top electrode, thus allowing greater collection of incident light. Responsivity of CTO-based MSM photodiodes with 1-μm finger widths and 2-μm finger spacings and without an AR coating between the electrodes was twice (0.62 A/W) that of a similar MSM photodiodes with Ti/Au electrodes (0.30 A/W). A thin 800 Å In0.52Al0.48 As layer was inserted below the electrodes to elevate the electrode Schottky barrier height. A digitally graded superlattice region (660 A) was also employed to reduce carrier trapping at the In 0.53Ga0.47As/In0.52Al0.48As heterointerface which acts to degrade photodiode bandwidth. Bandwidth of opaque electrode MSMs was elevated nearly an order of magnitude over a previous MSM photodiode design with an abrupt heterointerface, whereas the bandwidth of transparent electrode MSM's only improved about five times, indicating resistive effects may be intervening |
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