Contact Resistance of InGaN/GaN Light Emitting Diodes Grown on the Production Model Multi-Wafer MOVPE Reactor

Abstract

We report both the device fabrication and characterization of InGaN/GaN single quantum well LEDs grown on sapphire substrates using multi-wafer MOVPE reactor. To improve current spreading of the LEDs, a self-aligned process is developed to define LED mesa that is coated with a thin, semi-transparent Ni/Au (40 Å/40 Å) layer. A detailed study on the ohmic contact resistance of Ni/Cr/Au on p-GaN versus annealing temperatures is carried out on transmission line test structures. It was found that the annealing temperatures between 300 to 500 o C yield the lowest specific contact resistance r c ( 0.016 Ω-cm 2 at a current density of 66.7 mA/cm). Based on the extracted r c from the transmission line measurement, we estimate that the contact resistance of the p-type GaN accounts for ~ 88% of the total series resistance of the LED.

Low Resistance Optically Transparent Contacts to p–type GaN Using Oxidized Ni/Au and ITO for LED Application

“…A least squares curve fitting analysis of the data using this equation (a plot is shown in Figure 2) yielded a value for ρ c = 1.8 x 10 -3 Ω-cm 2 , an order of magnitude lower than the value typically reported for conventional thin Ni/Au annealed under N 2 [1]. …”

“…Around 40 Å of each metal are typically deposited and subsequently annealed under N 2 . These contacts exhibit ρ c values of around 1-2 x 10 -2 Ω-cm 2 [1]. Ho et al measured the level of optical transmission through a Ni/Au (100 Å /50 Å) bilayer on BK-7 glass, annealed at 500ºC under N 2 , as only around 30-35% between 400-500 nm [2].…”

Analysis of active matrix GaN-based HFET switch circuits integrated with GaN LED micro-displays

“…We use an automated integrated circuit modeling-Spice (AIM-SPICE) analog-circuit simulator to simulate the current waveforms flowing through the LED. The LED device parameters in this simulation are referred from [6] and [7] while HFET model is from [8], [9]. The series resistance of an LED is 26 and its threshold voltage is about 3.45 eV.…”