AVS 52nd International Symposium
    Electronic Materials and Processing Wednesday Sessions
       Session EM-WeA

Paper EM-WeA3
Polarization-enhanced Ohmic Contacts to GaInN-based Blue Light-Emitting Diodes

Wednesday, November 2, 2005, 2:40 pm, Room 309

Session: Contacts to Semiconductors
Presenter: T. Gessmann, Rensselaer Polytechnic Institute
Authors: T. Gessmann, Rensselaer Polytechnic Institute
Y.A. Xi, Rensselaer Polytechnic Institute
H. Luo, Rensselaer Polytechnic Institute
J.K. Kim, Rensselaer Polytechnic Institute
J.Q. Xi, Rensselaer Polytechnic Institute
K. Chen, Rensselaer Polytechnic Institute
E.F. Schubert, Rensselaer Polytechnic Institute
Correspondent: Click to Email
Thin p-type Ga@sub 1-x@In@sub x@N cap layers have been grown on p-type GaN contact layers of blue light emitting diodes (LEDs) using metal-organic vapor phase epitaxy (MOVPE) with an AIX 200/4 RF-S reactor. The Ga@sub 1-x@In@sub x@N cap layers have thicknesses smaller than 4 nm and In-contents varying between x = 0.1 and 0.2. The LED structure consists of a GaN nucleation layer grown on c-oriented sapphire, a 2 µm-thick n-type GaN layer, 5 Ga@sub 0.86@In@sub 0.14@N quantum wells embedded in GaN-barriers, and a 0.2 µm-thick p-type GaN layer. Having a cap layer thickness below the critical thickness of Ga@sub 1-x@In@sub x@N on GaN, a piezoelectric field will be present in the cap layer resulting in increased carrier tunneling probabilities through the metal-semiconductor barrier. The In-content and the strain status of the cap layers have been analyzed using HR X-Ray diffractometry. For cap layer thicknesses smaller than 4 nm, pseudomorphic Ga@sub 1-x@In@sub x@N has been obtained for three different In-contents x = 0.1, 0.15 and 0.2. LEDs have been fabricated using standard photolithograpy processes, CAIBE mesa etching and electron beam deposition of Ni/Au and Ti/Al/Ni/Au contact metals. The specific contact resistance, diode series resistance, ideality factor and optical output power of the LEDs are determined and compared to devices without capping layer. A specific contact resistance @rho@@sub c@ = 1.8 x 10@super -4@ @Ohm@ cm@super 2@ has been obtained for samples with InGaN cap layer; this value is significantly smaller than @rho@@sub c@ of a sample without cap layer. The results will be discussed in terms of a model relating the cap layer thickness and In-content to the p-type contact resistance.