Back‐Contacted Carrier Injection for Scalable GaN Light Emitters

Abstract

It has recently been proposed that back‐contacted III–V light‐emitting diodes (LEDs) could offer improved current spreading as compared to conventional mesa or double side contacted structures. This has inspired also experimental efforts to realize such structures, but fabrication methods for them have not yet been fully established. Herein, the use of unintentionally doped and partially carrier‐selective contacts (SC) is studied to realize back‐contacted indium gallium nitride (InGaN) LEDs. The sharp electroluminescence peak at 439 nm from the multiquantum well stack demonstrates that the approach allows fabricating back‐contacted InGaN LEDs without intentionally doped n‐GaN layers and without inflicting damage in the active region, often observed in alternative approaches relying on lateral doping and the use of high energy particles during fabrication. The samples are fabricated on a finger configuration with several finger widths between 1 and 20 μm. It is observed that the emission spreads most uniformly throughout the structure for fingers with the width of 5 μm. As shown by the simulations, with improved contact resistances, the structures reported herein could enable fabricating back‐contacted LEDs with unity injection efficiency and improved current spreading, offering a path toward large‐area LEDs without contact shading even in materials where n‐doping is elusive.

Back-Contacted GaInP/GaAs LED Structures by Ex-Situ Dopant Redistribution

“…The active device area used to calculate the average current densities through the devices is defined as the area of the p-mesa including the contact pad (1000 µm × 350 µm) and the area of the fingers calculated as W F × N × L F , which is slightly different for each device. Overall, the lateral dimensions of the studied devices here are similar to the recently reported GaN-based DDCT-LEDs [22].…”

“…Fabrication of compound semiconductor-based DDCT devices is not established due to the unconventional device structures and lack of appropriate lateral doping techniques. So far, experimental studies on DDCT-LEDs have focused merely on GaN devices [10], [21], [22], [23], [24], while GaAs devices have been considered only theoretically [7], [8], [9]. The first report of GaN-based DDCT-LEDs by Riuttanen et al [10] demonstrated the fundamental principle of DDCT by injecting holes into AR through an n-GaN layer.…”

“…The first report of GaN-based DDCT-LEDs by Riuttanen et al [10] demonstrated the fundamental principle of DDCT by injecting holes into AR through an n-GaN layer. More recently, Kim et al [22] proposed that n-contact of such structure could be placed directly on a thin i-GaN layer lowering the barrier for hole injection, while Lee et al [24] suggested lowering the barrier with ion implantation. In this work, we demonstrate the fabrication of back-contacted GaInP/GaAs double-heterojunction LEDs, as considered in our previous modeling work [7], and use drift-diffusion simulations to show that extending the p-doped region over originally lightly n-doped layers can reduce the barrier for hole injection despite the presence of a lateral p-n junction in GaInP.…”