Quantum Dot Laser Diodes emitting 1.57∼1.67μm at Room Temperature Grown by Block Copolymer Lithography and Selective Area MOCVD

Abstract

Semiconductor Laser diodes (LD) employing quantum dot (QD) active regions have attracted attention due to the theoretical predictions: low threshold current density and low temperature sensitivity originated from the delta-function-like density of states and small active volume [1]. However, while high performance devices have been demonstrated, the realization of all the predicted advantages has remained challenging. Self-assembled QDs grown by Stranski-Krastanov (SK) growth mode can suffer from an inhomogeneity in the QD size distribution, as well as an inherent wetting layer [2]. In particular, the InAs QD formation on InP substrates for the emission wavelength near the telecom C-band (1.55μm) remains quite challenging, compared to that emitting near telecom O-band (1.3 μm) grown on GaAs substrate because of the smaller driving force for the nucleation of InAs QDs, stemming from the smaller lattice mismatch on InP [3]. On the other hand, nanopatterning and selective metalorganic chemical vapor deposition (MOCVD) growth offer a more controllable pathway for QD formation, allowing the QD size to be decoupled from the strain state of the material. This process results in the formation of dense arrays of wetting-layer-free QDs, although the challenges stemming from surface state formation and efficient carrier injection into the QDs have remained problematic issues [4]. Here, we report the first demonstration of laser diodes operating at RT, employing an In 0.8 Ga 0.2 As QD active region formed by nanopatterning and selective growth on InP substrate. The QDs are formed in close proximity to an In 0.53 Ga 0.47 As carrier collecting QW, which are schematically represented in Fig. 1 (a). The LDs employ an active region consisting of a dense single-layer array of compressively-strained In 0.8 Ga 0.2 As QDs (Density ∼ 5–6× 1010 cm−2), as shown in Fig. 1. (b)