Title :
In0.53Ga0.47As MSM photodiodes with transparent CTO Schottky contacts and digital superlattice grading
Author :
Gao, Wei ; Berger, Paul R. ; Zydzik, George J. ; Bryan, Henry M O ; Sivco, Deborah L. ; Cho, Alfred Y.
Author_Institution :
Dept. of Electr. & Comput. Eng., Delaware Univ., Newark, DE, USA
fDate :
12/1/1997 12:00:00 AM
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
Keywords :
III-V semiconductors; Schottky barriers; cadmium compounds; gallium arsenide; indium compounds; metal-semiconductor-metal structures; photodiodes; semiconductor superlattices; Cd2SnO4; In0.53Ga0.47As; In0.53Ga0.47As MSM photodiode; Schottky barrier height; anti-reflection coating; digital superlattice grading; interdigitated electrode; optical window; transparent CTO Schottky contact; Bandwidth; Cadmium compounds; Coatings; Electrodes; Fingers; Optical superlattices; Photodiodes; Schottky barriers; Shadow mapping; Tin;
Journal_Title :
Electron Devices, IEEE Transactions on