In/sub 0.53/Ga/sub 0.47/As MSM photodiodes with transparent CTO Schottky contacts and digital superlattice grading

Wei Gao, Paul R. Berger, George J. Zydzik, Henry M. O'Bryan, Deborah L. Sivco, Alfred Y. Cho

Research output: Contribution to journalArticleScientificpeer-review

21 Citations (Scopus)


Metal-semiconductor-metal (MSM) photodiodes with an In0.53Ga0.47As 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 In0.52Al0.48As layer was inserted below the electrodes to elevate the electrode Schottky barrier height. A digitally graded superlattice region (660 Å) was also employed to reduce carrier trapping at the In0.53Ga0.47As/In0.52Al0.48As heterointerface which acts to degrade photodiode bandwidth. Bandwidth of opaque electrode MSM's 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. Publisher Item Identifier S 0018-9383(97)08292-0.

Original languageEnglish
Pages (from-to)2174-2179
Number of pages6
JournalIEEE Transactions on Electron Devices
Issue number12
Publication statusPublished - 1997
Externally publishedYes
Publication typeA1 Journal article-refereed

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Electrical and Electronic Engineering


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