ABSTRACT
ZnO is a direct and wide bandgap semiconductor with large exciton binding energy (60 meV), which shows a great promise for the application of high ef‹ciency and short wavelength light-emitting devices. ZnO has been investigated for many decades. Its lattice parameters have been known since 1935, whereas detailed optical studies have been carried out from the mid-1950s until now. But it has recently attracted much attention for optoelectronic and electronic devices due to the amenability to wet chemical etching, a high-radiation resistance, relatively low material costs, and the availability of large area ZnO substrates. Moreover, because of the large exciton binding energy, excitonic luminescence and lasing above room temperature are expected. These considerations lead
CONTENTS
7.1 Introduction ........................................................................................................................ 167 7.2 Optical Properties of Undoped ZnO Thin Films .......................................................... 168
7.2.1 Fundamental Optical Properties in ZnO ........................................................... 168 7.2.2 Depth-Resolved Optical Properties in ZnO ....................................................... 173 7.2.3 Optical Properties of ZnO Grown under Various Conditions ........................ 176
7.3 Optical Properties of p-Type ZnO ................................................................................... 180 7.3.1 N-Doped ZnO Epilayer ......................................................................................... 180 7.3.2 As-Doped ZnO Epilayer ....................................................................................... 181 7.3.3 P-Doped ZnO Epilayer .......................................................................................... 182 7.3.4 Sb-Doped ZnO Epilayer ........................................................................................ 184
7.4 Optical Properties of ZnO with Different Polarities .................................................... 186 7.4.1 Polarity-Controlled ZnO Epilayer ....................................................................... 186 7.4.2 O-Face and Zn-Face ZnO ...................................................................................... 189
7.5 Optical Properties of ZnO/ZnMgO Multiple Quantum Wells ................................... 190 7.5.1 Homoepitaxial ZnO/ZnMgO MQWs.................................................................. 190 7.5.2 Heteroepitaxial ZnO/ZnMgO MQWs ................................................................ 194
7.6 Summary ............................................................................................................................. 198 Acknowledgments ...................................................................................................................... 199 References ..................................................................................................................................... 199
researchers to actively pursue the development of ZnO-based optoelectronic devices. Since quantum well (QW) structures have been widely used in high-performance semiconductor optoelectronic devices, ZnO QWs have been actively investigated and show much larger optical gain compared with other semiconductors. Despite these advantages, applications of ZnO are hindered by the lack of reproducible, high-quality, and low-resistivity p-type ZnO due to the self-compensation and low solubility of dopants.
