Near-UV electroluminescence in unipolar-doped, bipolar-tunneling GaN/AlN heterostructures

Tyler A Growden,Elliott R Brown,Weidong Zhang,David J Meyer,David F Storm,Paul R Berger

doi:10.1038/lsa.2017.150

Abstract

Cross-gap light emission is reported in n-type unipolar GaN/AlN double-barrier heterostructure diodes at room temperature. Three different designs were grown on semi-insulating bulk GaN substrates using molecular beam epitaxy (MBE). All samples displayed a single electroluminescent spectral peak at 360 nm with full-width at half-maximum (FWHM) values no greater than 16 nm and an external quantum efficiency (EQE) of ≈0.0074% at 18.8 mA. In contrast to traditional GaN light emitters, p-type doping and p-contacts are completely avoided, and instead, holes are created in the GaN on the emitter side of the tunneling structure by direct interband (that is, Zener) tunneling from the valence band to the conduction band on the collector side. The Zener tunneling is enhanced by the high electric fields (~5 × 106 V cm−1) created by the notably large polarization-induced sheet charge at the interfaces between the AlN and GaN.

Highlights

Since the announcement of the first strong GaN blue-color lightemitting diodes (LEDs) by Nakamura et al in 1991 and 19931,2, interest in GaN photonics has grown steadily, and commercial applications have expanded to the extent that GaN devices are currently a viable industry
The p-type GaN contact remains a problem because it is difficult to grow and has low mobility for uniform carrier injection[3]. This feature becomes a bottleneck in design of GaN-based LEDs, and it is cited as the direct or indirect source of the ‘efficiency droop’ as LEDs are driven towards high brightness applications[4,5]
Instead of injection from a p-contact, holes tunnel into the radiative recombination region, that is, the n-doped GaN emitter, after they are generated by electron Zener tunneling from a valence-band quantum well, which occurs in the GaN spacer at the interface with the AlN barrier on the collector side of the heterostructure

Summary

INTRODUCTION

Since the announcement of the first strong GaN blue-color lightemitting diodes (LEDs) by Nakamura et al in 1991 and 19931,2, interest in GaN photonics has grown steadily, and commercial applications have expanded to the extent that GaN devices are currently a viable industry. One of the key steps forward by Nakamura et al was the development of a high-quality p-type GaN epitaxial layer using Mg as a dopant This process allowed the growth of a traditional p-n junction LED with qualities similar to those demonstrated in GaAs since the 1960s. The p-type GaN contact remains a problem because it is difficult to grow and has low mobility for uniform carrier injection[3] This feature becomes a bottleneck in design of GaN-based LEDs, and it is cited as the direct or indirect source of the ‘efficiency droop’ as LEDs are driven towards high brightness applications[4,5]. We emphasize that the Zener tunneling is greatly enhanced by the peculiar band bending in the GaN/AlN heterostructure and the resultant small valence-band AlN barriers for the holes in the GaN. We refer to this process as unipolar-doped, bipolar-tunneling (UDBT), and to the best of our knowledge, this is the first utilization of such an effect in optoelectronic devices of any sort

MATERIALS AND METHODS

RESULTS AND DISCUSSION

CONCLUSIONS