Strain Effects on Optoelectronic Devices

Abstract

Optoelectronics has become an essential part of modern lives in computer, consumer electronics, and communication. Optoelectronic devices either generate light or utilize light in their operation. Typical examples include light-emitting diodes in remote controls, battery chargers, even traffic lights, photodetectors in alarms, digital cameras, radars, and lasers in labs and barcode scanners in stores. Optoelectronics is based on the quantum mechanical interactions between light and matter, which in most cases are semiconducting materials. In these interactions, photons as energy quanta of the light are either emitted or absorbed. These two basic quantum processes are similar to the phonon transition processes in semiconductors, involving two electronic states with conservation of both energy and momentum. The energy of a photon is determined by its wavelength λ, E = hc/λ, where h is the Plank constant and c is the speed of light, and its momentum is given by h/λ. Photon energies for the visible light are between 2 and 3 eV, which is the range of semiconductor bandgaps, with their wavelengths between 4000 and 7000 Ǻ. Compared to the electron momentum hk in a solid, where k is the electron wave vector and in the order of π/a, where a is the lattice constant around the order of several Ǻ, the typical momentum of a photon is very small. Therefore, the photon transitions between electronic states in solids are considered “vertical.” That is to say, the electron momentum change for photon transitions in the Brillouin zone is often neglected, unlike the phonon processes. Also, phonons do not have angular momentum, but photons generally have definite polarization configuration and carry specific angular momentum, and thus angular momentum conservation has to be complied in photon transitions.