Owing to the high refractive index of semiconductors, light incident on a planar semiconductor- air interface is totally internally reflected, if the angle of incidence is sufficiently large. Snell’s law gives the critical angle of total internal reflection. As a result of total internal reflection, light can be “trapped” inside the semiconductor. Light trapped in […]

Current crowding also occurs in mesa-structure LEDs grown on insulating substrates. This type of LED includes GalnN/GaN LEDs grown on sapphire substrates. In these LEDs, the p-type contact is usually located on the top of the mesa, and the n-type contact is located on an n-type buffer layer at the bottom of the mesa. As […]

In LEDs with thin top confinement layers, the current is injected into the active region mostly under the top electrode. Thus, light is generated under an opaque metal electrode. This results in a low extraction efficiency. This problem can be avoided with a current-spreading layer that spreads the current under the top electrode to regions […]

LEDs may be grown on conductive and insulating substrates. Whereas the current flow is mostly vertical (normal to the substrate plane) in structures grown on conductive substrates, it is mostly lateral (horizontal) in devices grown on insulating substrates. The location and size of ohmic contacts are relevant to light extraction, because metal contacts are opaque. […]

It is imperative that the material comprising the active region of light-emitting devices is of very high crystal quality. Deep levels caused by point defects, unwanted impurities, dislocations, and other defects must have a very low concentration. Similarly, surface recombination must be kept at the lowest possible levels. This can be accomplished by keeping free […]

Doping of the confinement regions has a strong influence on the efficiency of double heterostructure LEDs. The resistivity of the confinement regions is one factor in determining the doping concentration in the confinement layers. The resistivity should be low to avoid resistive heating of the confinement regions. o’4 О c о й £ о с […]

The displacement of the p-n junction from its intended location into the cladding layer can be a significant problem in DH LED structures. Usually, the lower confinement layer is n-type, the upper confinement layer is p-type, and the active region is undoped or lightly doped with n — or p — type dopants. However, if […]

The lifetimes derived from the bimolecular rate equation show that the radiative rate increases with the free-carrier concentration for both the low excitation limit as well as the high excitation limit. It is therefore important that the region in which recombination occurs has a high carrier concentration. Double heterostructures are an excellent way to achieve […]

There are two general possibilities for attaining high internal quantum efficiency. The first possibility is to enhance the radiative recombination probability, and the second possibility is to decrease the non-radiative recombination probability. This can be accomplished in different ways which will be discussed below.

The derivation of the temperature dependence of the forward voltage presented here follows the analysis first given by Xi et al. (2004; 2005). The I-V characteristic of an ideal p-n junction diode is given by the Shockley equation 6.3 Theory of temperature dependence of diode forward voltage e Vf /(nidealkT) (6.3) — 1 J = […]