ABSTRACT
Zinc oxide (ZnO) is a wide, direct bandgap semiconductor (Eg = 3.3 eV at room temperature), attracting much interest in optoelectronic devices, such as light-emitting diodes, laser diodes, and photodetectors, due to a large exciton-binding energy of 60 meV [1,2]. An important step in designing optoelectronic devices is the bandgap engineering to produce barrier layers and quantum wells (QWs) in heterostructures as well as p-type doping under intensive study [3]. Modulation of the bandgap has been demonstrated by the development of Zn1−xCdxO and MgyZn1−yO systems [4,5]. However, there has been a big issue on structural phase transition from wurtzite to rock salt with increasing alloy content in contrast to the Ga(In,Al)N ternary system. While, in particular, wurtzite Zn1−xCdxO has been examined by laser and/or conventional molecular beam epitaxy (MBE) [5-7], and conventional metal-organic chemical vapor deposition (MOCVD) [8-10], it is well known that it is dif‹cult for growing wurtzite Zn1−xCdxO system with high Cd content. In order to overcome this problem, we have developed a remote-plasma-enhanced metal-organic
CONTENTS
11.1 Introduction ........................................................................................................................ 321 11.2 Growth System and Peripherals ...................................................................................... 322
11.2.1 Remote-Plasma-Enhanced Metal-Organic Chemical Vapor Deposition ....... 322 11.2.2 Characterizations ................................................................................................... 324
11.3 Characteristics of Zn(Mg,Cd)O Alloys ........................................................................... 324 11.3.1 Structural Properties ............................................................................................. 325 11.3.2 Optical Bandgap and PL Energy ......................................................................... 326 11.3.3 PL Alloy Broadening ............................................................................................. 328
11.4 Characteristics of Zn0.85Cd0.15O/ZnO MQWs .................................................................333 11.4.1 Structural Properties .............................................................................................334 11.4.2 Optical Properties ..................................................................................................335
