Journal of Non-Crystalline Solids 137&138 (1991) 126%1270 North-Holland ]OURNA L OF NON-CRYSTALLINE SOLIDS INFRARED-INDUCED PHOTOCONDUCTIVITY AND ELECTROLUMINESCENCE IN FORWARD-BIASED a-Si:H PIN-DIODES JSrg WIND* and Gerhard MULLER *Technical University of Munich, Physics Dept. El6, 8046 Garching, FRG Messerschmitt-B~ikow-Blohm GmbH, Postfach 80 ii 09, 8000 M~nchen 80, FRG The electronic properties of a-Si:H pin diodes have been investigated under conditions of forward-bias and low-temperature operation. Our experiments demonstrate that, under these conditions, a-Si:H pin diodes can respond to infrared (IR) radiation (i) through an enhancement in the diode currents and, (ii) through an enhancement in the electroluminescence signal. We propose that the IR photoeffect is due to the re-excitation of band-tail trapped excess carriers injected into the localized conduction and valence band tail states in the vicinity of the n + and p+ contact regions. i. INTRODUCTION In dual-beam photoconduction experi- ments a beam of visible light is used to excite charge carriers across the mobility gap and IR light is used to re-excite band-tail trapped charge car- riers to the respective mobility edges. Previous work 1,2 has established that, under these conditions, a-Si:H films can exhibit a long-wavelength photores- ponse out to about X = 8~m provided the optical pumping is performed at tempe- ratures sufficiently low to immobilize the non-equilibrium charge carriers in localized band-tail states. In the pre- sent work we have replaced optical pum- ping by double-injection into the cen- tral i-layer of a pin-diode and obser- ved a long-wavelength photoresponse in a typical device configuration. 2. EXPERIMENTAL DETAILS The p-i-n junctions used in this work consisted of the layer sequence glass/ITO/pin/Al with the light ente- ring through the glass substrate. The possible long-wavelength response of these devices is limited by the strong absorption of the 7059 Corning glass substrates for X > 2.7~m and by the plasma absorption of the conducting ITO contacts which occurs in the same wave- length region. The junction area, defi- ned by the dimensions of the overlap of the A1 and ITO contacts, was 6mm 2. De- position parameters were similar to those of photovoltaic junctions except for the thickness of the i-layer which was varied in the range 0.1~m<di<l~m. Photoelectric measurements were per- formed on these junctions in the tempe- rature range 10K<T<300K under dc condi- tions. In those cases where lock-in techniques had to be employed the chop- per frequency was reduced to f=5Hz in order to minimize ac effects. In the case of C-V measurements reasonably noise-less measurements could only be taken above f=500Hz. 0022-3093/91/$03.50 © 1991 - Elsevier Science Publishers B.V. All rights reserved.