Optimization of Electroluminescent Efficiencies for Vapor-Grown GaAs[sub 1−x]P[sub x] Diodes

Abstract

A series of GaAs1−xPx diodes have been prepared by a vapor‐phase growth technique to investigate the effects of current‐spreading, absorption, impurity concentrations, and alloy composition on room‐temperature electro‐luminescent efficiencies. It is shown that for maximum efficiencies, a diode structure should be prepared with a p+ surface layer to enhance current spreading, and a GaAs1−xPx “window” containing about 10% more normalGaP than the p‐n junction region to reduce absorption losses. It is also shown that the most efficient radiative recombination originates on the p‐side of the junction; low acceptor concentrations and high donor concentrations which are required for strong electron injection into the p‐side of the junction are thus found to result in highest electroluminescent efficiencies. Slow compositional grading between the normalGaAs substrate and the GaAs1−xPx p‐n junction also resulted in increased efficiencies. A drop‐off in efficiency near the direct‐indirect transition for values of x increasing from 0.38 was found to be severe, however, a corresponding increase in the spectral sensitivity of the eye was found to provide a broad maximum in diode brightness at emission wave‐lengths near 6800Aå ( x≈0.38 ). Planar uncoated diodes have provided brightness values in excess of 300 ft‐L at 10 amp/cm2 with external efficiencies of 2×10−4 at 6400Aå. Plastic encapsulants ean be readily used as domes to increase external efficiencies by a factor of 3, or as directional lenses to provide beam‐widths as narrow as 7°.

Inorganic Semiconductors for Light‐emitting Diodes

“…The usefulness of current-spreading layers was shown by Nuese et al [25] who demonstrated a substantial improvement of the optical output power in GaAsP LEDs. The effect of the current-spreading layer is illustrated schematically in Fig.…”

Vapor phase epitaxial materials for LED applications

“…I t must be remembered, however, that as the Zn concentration increases there is a tradeoff between reducing 7~ and ~N R . Also, if the Zn concentration is increased to too high of a level, hole injection into the n-type region can occur which is largely nonradiative [74]. The Zn profile which is optimum for one type of material may not be suitable for another.…”

Improvement of the light extraction efficiency in light emitting diodes (LEDs) using ray trace

“…Therefore the key to increasing the e¢ ciency of an LED , should focus on improvments to the LEE. Various solutions for improvement have been studied such as creating a spherical dome enclosure for the LED system [3,4], the use of photonic crystal substrates in combination with the semiconductor substrates [5], and thin …lm surface roughening of the semiconductor substrates [6,7]. We look into the geometric designs that could lend increases to the LEE, extr , for future LEDs using ray trace simulations via Ligh Tools.…”