High Optical Response in Forward Biased (In,Ga)N–GaN Multiquantum-Well Diodes Under Barrier Illumination

The authors report on the current-voltage (I-V) characteristic under forward biases obtained in low leakage, small size p-(In,Ga)N-GaN-n multiquantum well diodes. Under barrier illumination, the devices present a high optical response with capabilities to detect optical powers in the pW range without further amplification. This response is attributed to the screening of the internal electric fields. Recombination times of a few seconds are found to be associated to this mechanism. Moreover, a step-like feature is found in the I-V characteristic before the diode turn-on voltage. Our model proposes tunneling current through the multiquantum-well structure as responsible of this feature. Fast modulation of the tunneling effect under barrier illumination is used to evaluate the detection of low photon fluxes.

I. Introduction

From the first investigations in III-nitride semiconductors, the high responsivities observed in GaN photoconductors and the associated gain mechanisms attracted the attention of many groups [1]–[3]. Other structures and photocurrent gain mechanisms have been also studied in order to satisfy the need of high sensitivity ultraviolet (UV) detectors for visible- and solar-blind applications. Examples of this research are: carrier multiplication in avalanche photodiodes [4], [5], minority carrier trapping in Schottky barrier photodiodes [6], and more recently, piezoelectric field engineering in multiple-quantum-well (MQW) detectors [7]. However, only avalanche multiplication has demonstrated high enough gain to show single photon detection capabilities [8], [9].