IN0.53CA0.47AS MSM PHOTODIODES WITH TRANSPARENT CTO SCHOTTKY CONTACTSAND DIGITAL SUPERLATTICE GRADING

Metal-semiconductor-metal (MSM) photodiodes with an In0.53Ga0.47As act ive region were investigated using a transparent cadmium tin oxide (CT O) layer for the interdigitated electrodes to improve the low responsi vity of conventional MSM photodiodes with opaque electrodes, CTO is su itable as a Schottky contact, an optical window and an anti-reflection (AR) coating, The transparent contact prevents shadowing of the activ e layer by the top electrode, thus allowing greater collection of inci dent light, Responsivity of CTO-based MSM photodiodes with 1-mu m fing er widths and 2-mu m 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 Angstrom In0.52Al0.48As layer was inserted below the electrodes to elevate the electrode Schot tky barrier height, A digitally graded superlattice region (660 Angstr om) was also employed to reduce carrier trapping at the In0.53Ga0.47As /In0.52Al0.48As heterointerface which acts to degrade photodiode bandw idth, Bandwidth of opaque electrode MSM's was elevated nearly an order of magnitude over a previous MSM photodiode design with an abrupt het erointerface, whereas the bandwidth of transparent electrode MSM's onl y improved about five times, indicating resistive effects may be inter vening.