Influence of Carrier Lifetime, Transit Time, and Operation Voltages on the Photoresponse of Visible-Blind AlGaN Metal--Semiconductor--Metal Photodetectors

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We investigated the influence of lifetime and transit time of photogenerated carriers on the performance of visible-blind Al<inf>0.25</inf>Ga<inf>0.75</inf>N metal--semiconductor--metal photodetectors by a combination of experimental studies and numerical simulations. Good agreement between simulated and measured current--voltage (I--V) characteristics was achieved for several geometries of the interdigitated contact structure. Simulations of the external quantum efficiency (EQE) at low bias voltages showed that a long hole lifetime in the AlGaN absorption layer significantly influences the EQE due to the slow carrier transit in weak electric fields. At 1 V the EQE can be enhanced by a factor of 3 by increasing the hole lifetime from 10 ps to 1 ns. Reducing the electrode spacing from 10 to 1 μm as well as operating the device at higher voltages additionally increases the ratio between carrier lifetime and transit time, resulting in an enhancement of the EQE at a fixed carrier lifetime by one order of magnitude.
2013-08-25