Estimation of carrier leakage in InGaN light emitting diodes from photocurrent measurements Shopan Hafiz *a , Fan Zhang a , Morteza Monavarian a , Serdal Okur a , Vitaliy Avrutin a , Hadis Morkoç a , and Ümit Özgür a a Department of Electrical and Computer Engineering, Virginia Commonwealth University, Richmond, Virginia 23284, USA ABSTRACT Carrier transport in double heterostructure (DH) InGaN light emitting diodes (LEDs) was investigated using photocurrent measurements performed under CW HeCd laser (325 nm wavelength) excitation. The effect of electron injector thicknesses was investigated by monitoring the excitation density and applied bias dependent escape of photogenerated carriers from the active region and through energy band structure and carrier transport simulations using Silvaco Atlas. For quad (4x) 3-nm DH LED structures incorporating staircase electron injectors (SEIs), photocurrent increased with SEI thickness due to reduced effective barrier opposing carrier escape from the active region as confirmed by simulations. The carrier leakage percentile at -3V bias and 280 Wcm -2 optical excitation density increased from 24 % to 55 % when In 0.04 Ga 0.96 N + In 0.08 Ga 0.92 N SEI thickness was increased from 4 nm + 4 nm to 30 nm + 30 nm. The increased leakage with thicker SEI correlates with increased carrier overflow under forward bias. Keywords: Carrier leakage, Carrier overflow, Photocurrent, InGaN LED, Staircase electron injector. 1. INTRODUCTION The performance of InGaN-based light emitting diodes (LEDs) has improved significantly over the last few decades. However, reduction of efficiency at high injection current is the main limiting factor for InGaN-based LEDs to be used in general lighting. 1 Different mechanisms such as Auger recombination, 2 electron overflow, 3,4,5 carrier delocalization and nonradiative recombination at defects, 6,7 junction heating effects, 8 have been proposed to be responsible for this efficiency loss but among these, carrier overflow is considered to be one of the most probable one. Escape of carriers from the active region in forward bias is known as carrier overflow while in reverse bias it is termed as carrier leakage. Calculation of carrier overflow from band structure simulation has already been reported. 9 In this paper, quad (4x) double heterostructure (DH) InGaN LEDs with different electron injector thicknesses were investigated in order to quantify the carrier leakage and correlate that information to carrier overflow. 2. EXPERIMENTAL PROCEDURE The c-plane InGaN LED structures were grown on ~3.7 µm-thick n-type GaN templates on sapphire in a vertical low- pressure metalorganic chemical vapor deposition (MOCVD) system. The active region was composed of four 3nm-thick In 0.15 Ga 0.85 N active regions separated by 3nm In 0.06 Ga 0.94 N barriers (quad 3 nm DH). A 60-nm Si-doped (2×10 18 cm 3 ) In 0.01 Ga 0.99 N underlying layer was grown just beneath the active region for improving the quality of the overgrown layers. All the structures feature a staircase electron injector (SEI) layer for efficient thermalization of hot carriers prior to injection into the active region. The SEI consists of two InGaN layers (4 nm, 20 nm or 30 nm each) with step increased Indium compositions of 4% and 8%, inserted in the given order below the active region. The LED structures were completed with Mg-doped p-GaN layer of 100-nm thickness having 4×10 17 cm 3 hole density, as determined by Hall measurements on a separate calibration sample. Light-Emitting Diodes: Materials, Devices, and Applications for Solid State Lighting XVIII, edited by Klaus P. Streubel, Heonsu Jeon, Li-Wei Tu, Martin Strassburg, Proc. of SPIE Vol. 9003, 90031R © 2014 SPIE · CCC code: 0277-786X/14/$18 · doi: 10.1117/12.2040926 Proc. of SPIE Vol. 9003 90031R-1 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 01/13/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx