Site Control and Selective-Area Growth Techniques of In As Quantum Dots with High Density and High Uniformity

Abstract

The internet requires ever more rapid transmission of huge amounts of information in optical communication systems as its use becomes more and more widespread.We have been studying ultrafast devices for optical time-divisionmultiplexing. Ultrafast demultiplexing has been reported with a symmetric- Mach–Zehnder-type (SMZ) all-optical switch by Tajima et al. [1,2], where the switching speed is not restricted to the carrier lifetime of optical nonlinear materials. Since this device was a 20-mm-long hybrid system, it is important to miniaturize it into monolithic ultrasmall devices of 1mm square. To approach this target, we have been studying photonic-crystal-based SMZ (PCSMZ) all-optical switches with quantum dots (QDs) as an optical nonlinear material [3, 4] as shown in Fig. 17.1. Very recently, we have demonstrated picosecond switching in the PC-SMZ all-optical switch [5]. In this device, QDs should be located only in the phase-shift regions, and it is. therefore necessary to develop new techniques to selectively grow uniform high-density QDs only in required regions. These requirements for QDs are also essential for other devices such as lasers [6], semiconductor optical amplifiers [7], and single QD devices [8, 9].

In this chapter, we cover our new techniques for site control and selectivearea growth of InAs QDs of high density and high uniformity. In Sects. 17.2.1– 17.2.2, we report a method to produce uniform high-density self-assembled QDs and their selective growth using in-situ masking.