Room temperature operation of InAs quantum dot lasers formed by diblock-copolymer lithography and selective area MOCVD growth

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]. 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 remain problematic issues [3]. As such, previously reported LDs employing these In0.3Ga0.7As QD active regions only operate at low temperatures [3]. It has been contended that embedding the SK QDs within an InGaAs quantum well (QW) improves carrier capture into the quantum dots [4]. Here, we demonstrate an In0.1Ga0.9As QW placed adjacent to a wetting layer-free InAs QD active region leads to improved active region carrier collection, allowing for room temperature (RT) lasing. The LDs employ an active region consisting of a dense single-layer array of compressively-strained InAs QDs (Density ∼ 4×1010cm−2), selectively grown by MOCVD on top of a 4nm thick In0.1Ga0.9As QW.