The total enhancement integrated over wavelength, rather than the enhancement at the resonance wavelength, is relevant for many practical devices. On resonance, the emission is enhanced along the axis of the cavity. However, sufficiently far off resonance, the emission is suppressed. Because the natural emission spectrum of the active medium (without a cavity) can be […]

Because the emission rate at a given wavelength is directly proportional to the optical mode density (see Eq. 14.7), the emission rate enhancement spectrum is given by the ratio of the 1D cavity mode density to the 1D free space mode density. As calculated earlier, the cavity enhancement spectrum has a lorentzian lineshape. The enhancement […]

In this section, the enhancement of spontaneous emission will be calculated based on the changes of the optical mode density in a one-dimensional (1D) resonator, i. e. a coplanar Fabry-Perot microcavity. We first discuss the basic physics causing the changes of the spontaneous emission from an optically active medium located inside a microcavity and then […]

The simplest form of optical cavity consists of two coplanar mirrors separated by a distance Lcav. About one century ago, Fabry and Perot (1899) were the first to build and analyze optical cavities with coplanar reflectors. These cavities had a large separation between the two reflectors, i. e. Lcav >> X. However, if the distance […]

14.1 Modification of spontaneous emission Radiative transitions, i. e. transitions of electrons from an initial quantum state to a final state and the simultaneous emission of a light quantum, are one of the most fundamental processes in optoelectronic devices. There are two distinct ways by which the emission of a photon can occur, namely by […]

Diodes emitting at wavelengths less than 360 nm have AlGaN active regions or AlxGa1-xN/ AlyGa1-yN multiple-quantum well (MQW) active regions. The power efficiency of these devices is generally low, i. e. less than 1%, although substantial progress has been made in recent years (Zhang et al., 2002a, 2003; Yasan et al., 2002; Kipshidze et al., […]

UV devices emitting at wavelengths longer than 360 nm generally have GaN or GaInN active regions. GaInN LEDs with peak wavelengths ranging from 400 nm to 410 nm were reported as early as 1993 (Nakamura et al., 1993a, b, 1994). The design of an early GaInN UV LED emitting at 370 nm is shown in […]

The most common substrate for GaN epitaxial growth, sapphire, is a very stable substrate in terms of its thermal, chemical, and mechanical properties. However, sapphire has the complex corundum structure whereas III-V nitrides crystallize in the wurtzite structure. Furthermore, the lattice constants of sapphire and GaN are different. As a result, GaN epitaxial films have […]

Another problem in III-V nitrides is the low doping activation, which is caused by two effects: (i) Chemical deactivation of acceptors by hydrogen atoms bonding to the acceptors. The missing electron that acceptors strive to capture is provided by a hydrogen atom. Hydrogen is available in abundance during epitaxial growth and possible sources for hydrogen […]

The most common epitaxial growth direction of III-V nitrides is the с-plane of the hexagonal wurtzite structure. III-V nitrides grown on the с-plane have polarization charges located at each of the two surfaces of a layer. As a result of these charges, internal electric fields occur in III-V nitrides that have a significant effect on […]