GaN-based Photodiodes on Silicon Substrates

Abstract

GaN-based or the III-V nitrides materials are wide band gap semiconductor materials with dormant utilizations in optoelectronic as well as in electronic devices operating at high power and high temperature conditions. Silicon (Si) is one of the most common elements of the earth crust and the substrates are of very low price and are available in very large size due to its mature development and large-scale production. The thermal conductivity is higher than that of sapphire and is close to that of GaN. The crystal perfection of Si is better than that of any other substrate material and it has good thermal stability under GaN epitaxial growth condition. The growth of GaN on Si enables the possibility of integrating GaN optoelectronics devices with Si-based electronics. However, despite much effort, there is no significant breakthrough that has been obtained because of the high density of dislocations in these materials leading to a rapid degradation of all devices fabricated so far. In contrast, the performances of GaN-based devices are known to be quite acceptable despite the large density of dislocations present in the films. There are only few reports on GaN photodetectors on Si(111), including PN heterojunction photodiode, metalsemiconductor-metal (MSM) photodetectors, and Schottky photodiodes. This chapter will present the fabrication and characterization aspects of GaN-based photodiodes on Si substrates. Photodetectors operating in the UV and with a visible blind behavior have drawn great attention in recent years, with a number of applications in both civil and military industries which include detection of missile plumes, flame sensors, engine control, solar UV monitoring, source calibration, UV astronomy, and secure space-to-space communications (Keem et. al., 2004; Hassan et. al., 2004). Contrast to Si, gallium nitride (GaN) has wide band gap, outstanding thermal stability, small dielectric constant, chemical inertness and radiation hardness. These features make it an typical choice for use in fabricating high frequency, high power electronic devices. Furthermore, the essential preference of III-V nitrides detectors above competing devices based on semiconductors with smaller bandgaps is the long wavelength response cut-off, which is straightly associated to the bandgap of the material in the dynamic area and consequently, does not involve external filters (BenMoussa et. al., 2008). Gallium nitride (GaN) is of distinguished interest because of its great UV photoresponse, well-founded mixture techniques, and the capability of operating at high temperature and in harsh