Light-emitting diodes (LEDs) are devices designed to efficiently convert electrical energy into electromagnetic radiation, most of which is visible to the human eye. Some of the disciplines involved in the understanding and utilization of LEDs are reviewed, with emphasis on the III-V semiconducting compounds and GaP LEDs in particular. Salient features of photometry, the physics of electrical injection and luminescence, and the design of LEDs are discussed in detail, followed by a survey of prominent applications for the various LEDs.

Light-emitting diodes

This article reviews recent progresses in our understanding of the mechanisms of Ga self-diffusion and impurity diffusion in GaAs, and of the disordering of GaAs/AlGaAs superlattices. Gallium self-diffusion and AI-Ga interdiffusion under intrinsic and n-doping conditions are governed by the triply negatively charged group 111 sublattice vacancies V 3- Ga, while under heavy p-doping conditions most likely by the doubly positively charged self-interstitial I 2+ Ga. The GaAslAIGaAs superlattice disordering enhancement observed under n-doping by Si or by Te is due to the Fermi-level effect that increases the V 3- Ga concentration, while the observable or not observable disordering enhancement under p-doping by Zn or by Be is due to the combined effects of the Fermilevel, which increases the I 2+ Ga concentration, and the dopant in-diffusion or out-diffusion induced I 2+ Ga supersaturation or undersaturation. respectively. In consistency with the Ga self-diffusion mechanism in GaAs, diffusion of the S...

Point defects, diffusion mechanisms, and superlattice disordering in gallium arsenide-based materials

The effects of low‐energy ion bombardment on enhancing elemental diffusion rates at both heterojunction interfaces during film deposition and over the compositionally altered layer created during sputter etching alloy targets have been considered. Depth dependent enhanced interdiffusion coefficients, expressed as D*(x)=D*(0) exp(−x/Ld), where D*(0) is more than five orders of magnitude greater than thermal diffusion values, were measured in InSb/GaSb multilayer structures deposited by multitarget bias sputering. D*(0) was determined from the amplitude u of the compositional modulation in the multilayered films (layer thicknesses between 20 and 45 A) as measured by superlattice x‐ray diffraction techniques. The value of D*(0) was found to increase from 3×10−17 to 1×10−16 cm2/sec as the applied substrate bias was increased from 0 to −75 V. However even at Va=0, the diffusion coefficient was enhanced owing to an induced substrate potential with respect to the positive space‐charge region in the Ar discharge....

Diffusion enhancement due to low‐energy ion bombardment during sputter etching and deposition

The influence of dislocations on the radiative recombination of electron‐hole pairs in GaAs and InP is investigated by spatially resolved photoluminescence measurements. The shape of the spectra is unchanged at individual dislocations, while the overall intensity is lowered by about 30% in a region of 5–10 μm around the dislocations. This relative change of intensity is temperature independent in the investigated range 10–300 K. Deformation‐induced dislocations, prepared by plastic deformation at 600 °C, behave similarly to as‐grown dislocations. These statements hold for 60° dislocations and screw dislocations in both n‐type and p‐type material. Search for dislocation‐induced electronic levels in the band gap by deep‐level transient spectroscopy, optical absorption, and photoluminescence of GaAs samples with very high dislocation density gives no evidence for such levels. Our findings suggest that the quenching of the radiative recombination near dislocations is caused by an enhancement of the nonradiati...

Photoluminescence at dislocations in GaAs and InP

Publisher Summary This chapter explores that qualitative or semi-quantitative understanding of the factors determine hole mobilities It discusses the results of numerical calculations, which suggests improvements in the phenomenological expressions presented in the chapter, and allow an assessment of the use of Matthiessen's rule in combining hole mobilities Even the most elaborate theoretical models cannot be fairly tested until there are more reliable values for some of the material parameters The most outstanding examples of poorly known parameters are the valence band parameters, the heavy-hole effective masses, and the deformation potentials Present crystal growth technology should allow the growth of high-quality films, although sample preparation and handling are made difficult by the high reactivity of these materials With the exception of GaAs and InSb, the electrical properties of the p-type III-V compounds have been studied only over a narrow range of impurity concentrations and there has been no critical test of the theory of ionized-impurity scattering This is an area in which there is room for further work in materials preparation as well as experimental and theoretical evaluation

Chapter 2 Mobility of Holes in III-V Compounds

Of the various compound semiconductors, the III–V compounds have properties most similar to the group IV elemental semiconductors. Like Si and Ge, the III–V compounds may readily be doped as n- orp-type to form p-n junctions, the most useful and widespread application of semiconductors. They are 1-to-l chemical compounds of the group III elements B, Al, Ga, and In with the group V elements N, P, As, and Sb. The III–V compounds are tetrahedrally coordinated, and the majority crystallize in the zinc-blende structure illustrated in figure 6.1 for GaAs. The zinc-blende structure is the diamond lattice of Si or Ge, but with group III and V atoms occupying adjacent lattice sites. Although the diamond and zinc-blende structures are similar, the differences in lattice constant, the presence or absence of d-shell electrons, and the ionicity of the III–V compounds result in significant differences in the band structure [1]. The varied band structures and large range of energy gaps possible with the III–V compounds have led to many potential applications. The crystal structure, lattice constant, type of energy gap, and the room temperature energy gap are summarized in Table 6.1 for the elemental semiconductors Si and Ge and the III–V compound semiconductors.

H. C. Casey

Papers

Diffusion in the III–V Compound Semiconductors