Optoelectronic Devices: III Nitrides

Mohamed Henini, M Razeghi

• Publisher: Elsevier Science
• Year: 2004
• ISBN:
  9780080538112
• Topic: Physical Sciences
• Subtopic: Nanoscience

Tremendous progress has been made in the last few years in the growth, doping and processing technologies of the wide bandgap semiconductors. As a result, this class of materials now holds significant promis for semiconductor electronics in a broad range of applications.

The principal driver for the current revival of interest in III-V Nitrides is their potential use in high power, high temperature, high frequency and optical devices resistant to radiation damage.

This book provides a wide number of optoelectronic applications of III-V nitrides and covers the entire process from growth to devices and applications making it essential reading for those working in the semiconductors or microelectronics.

• Broad review of optoelectronic applications of III-V nitrides

Chapter 1

Introduction

M. Razeghi^a[email protected], ^aDepartment of Electrical and Computer Engineering, Center for Quantum Devices, Northwestern University, Cook Room 4051, 2220 Campus Drive, Evanston, IL 60208-3129, USA

M. Henini^b[email protected], ^bSchool of Physics and Astronomy, University of Nottingham, NG7 2RD, UK

Publisher Summary

Wide bandgap III-nitrides—including (AI,Ga,In)-N—have seen enormous success in their development especially, in the latest stages of 20th century. Many substantial problems had to be overcome before these materials could constitute useful devices. High density of dislocations because of the lack of lattice-matched substrates and low doping efficiency were the most challenging problems that researchers in this area had to face. Today blue/violet light-emitting diodes and laser diodes based on (Al,In,Ga)-N have been successfully commercialized. Blue/green light emitting diodes (LEDs) have already found their market in full-color liquid crystal displays (LCDs) and traffic lights. The unique properties of III-nitrides lead to a range of applications from optoelectronic devices to high-power electronics. The wide bandgap of gallium nitride (GaN) makes this material suitable not only for light emitting source but also for high-temperature applications. GaN and its alloys have the potential for forming high power electronics such as transistors or thyristors. Ultraviolet solar-blind photodetectors based on AlGaN have applications in early missile threat detection and interception, chemical and biological threat detection, UV flame monitoring, and UV environmental monitoring. There are some other conceivable applications for III-nitrides such as surface acoustic wave generation, acousto-optic modulator, and devices that utilize negative electron affinity.

1.1 INTRODUCTION

Wide bandgap III-nitrides, including (AI,Ga,In)-N, have seen enormous success in their development especially in the latest stages of the 20th century. Many substantial problems had to be overcome before these materials could constitute useful devices. High density of dislocations due to the lack of lattice-matched substrates and low doping efficiency were the most challenging problems that researchers in this area had to face. At the beginning, it was hard to believe that a material with a dislocation density in the order of 10⁸–10¹⁰ cm⁻² would become the building block of many viable devices. However, thanks to the hard work of researches in this field, today blue/violet light-emitting diodes and laser diodes based on (Al,In,Ga)-N have been successfully commercialized. Blue/green LEDs have already found their market in full-color LCD displays and traffic lights, while blue LDs are expected to shortly replace red lasers in the current CD/DVD read/write systems. The unique properties of III-nitrides lead to a range of applications from optoelectronic devices to high-power electronics. The wide bandgap of GaN makes this material suitable not only for light emitting source but also for high-temperature applications. GaN and its alloys have the potential to form high power electronics such as transistors or thyristors. UV solar-blind photodetectors based on AlGaN have been demonstrated by several groups [1]. These detectors have applications in early missile threat detection and interception, chemical and biological threat detection, UV flame monitoring, and UV environmental monitoring. Due to the polar nature of the Ga-N bond, GaN does not possess inversion symmetry. Thus, when GaN is subject to an alternating electric field, the induced polarization is not symmetric. This property of GaN can be used in non-linear optics applications such as second-harmonic generation [2]. The same lack of inversion symmetry results in a huge piezoelectric field. There are some other conceivable applications for III-nitrides such as surface acoustic wave generation [3], acousto-optic modulator [4], and devices that utilize negative electron affinity [5].

Group III-nitride materials are different from some conventional semiconductors such as silicon (Si) and GaAs in a sense that under ambient conditions, the thermodynamically stable structure is wurtzite. Although zinc blende structure for GaN or InN could exist by forcing the film to grow on {001} crystal planes of cubic substrates, the intrinsic tendency of III-nitrides is to form a wurzite structure with a hexagonal symmetry. The large difference in electronegativity between the group III elements and nitrogen (Al = 1.18, Ga = 1.13, In = 0.99, N = 3.0) leads to very strong chemical bonds in III-nitride material system which together with a wide direct energy gap is the origin of some interesting properties of III-nitrides [6].

III-nitrides have a bandgap energy tunable from 6.2 eV for AIN to 3.4 eV for GaN to 2 eV or below for InN (The energy gap of InN has been the subject of many debates and it is not agreed upon yet. There have been some recent reports on the bandgap energy of InN being as narrow as 0.7 eV) [7,8]. This corresponds to a wavelength range of 200–650 nm or higher, covering a broad spectral range, from UV to visible.

Figure 1.1 demonstrates where III-nitride compound semiconductors stand compared to other semiconductors in the space of lattic...