Heterostructure Photonic Devices

Abstract

The light emitters made of III–V alloys are the most important and widely used photonic devices because Si and Ge do not emit light due to their indirect band structures. The semiconductor laser is similar to the solid-state ruby laser and Ar⁺ gas laser in that the emitted radiation is highly monochromatic and produces a highly directional beam of light. However, the semiconductor laser is much smaller (on the order of 0.25 mm long) than other lasers and is easily modulated at high frequencies simply by modulating the injected current. Because of these unique properties, the semiconductor laser is one of the most important light sources for optical-fiber communication. It also has many applications in consumer electronics such as optical reading, laser printing, and face ID, to mention just a few. In addition, semiconductor lasers have significant applications in many areas of basic research and technology, such as high-resolution gas spectroscopy and atmospheric pollution monitoring. A related important photonic device is the light-emitting diode (LED), which has a device structure very similar to the semiconductor injection laser but without a resonant optical cavity. Today, visible LEDs play a leading role in displays and solid-state lighting applications. In this chapter, the device physics, structures, and characteristics of many types of heterostructure lasers are discussed. The current status and challenges of visible LEDs are briefly reviewed. In addition, the quantum cascade laser based on unipolar inter-subband transitions for long-wavelength applications is introduced. Also discussed is the mid-infrared quantum-well infrared photodetector, operating based on the same unipolar inter-subband optical transition. Finally, the concept of optoelectronic integration is demonstrated in the transistor laser where both transistor and laser operation are realized simultaneously in the same device.