Violet–green laser converter based on MBE grown II–VI green lasers with multiple CdSe quantum dot sheets, pumped by InGaN laser diode

Abstract

The violet-green laser converter based on a molecular-beamepitaxy (MBE) grown CdSe quantum dot (QD) laser heterostructure pumped by a commercial InGaN laser diode (LD) emission has been fabricated and studied in detail. The optimized II-VI laser heterostructure consists of asymmetrical ZnSe/ZnSSe superlattice (SL) waveguide and active region comprising five CdSe QD sheets (QDS) placed in the centre of 2-nm-thick ZnSe quantum wells. The new laser structure design provides both a high homogeneity of optical pumping of the CdSe QDS due to tunnelling of charge carriers between the QDS separated by 5-nm-thick ZnSe/ZnSSe/ZnSe barriers and high optical confinement factor. Optimization of both cavity length of the II-VI laser and parameters of optical focusing system to obtain a narrow stripe with the length slightly exceeding the cavity length has been performed. As a result, the maximum achieved quantum efficiency and pulse output power in green have been as high as 8% and 65 mW, respectively.

Microchip laser converter based on InGaN laser diode and (Zn)CdSe quantum dot heterostructure

“…Assuming that exciting stripe width d is fixed, the threshold pumping power of optically pumped QW laser could be expressed in the following form [14]:…”

Violet-green electrically pumped laser converters with output power over 150 mW

“…A concept of stress compensation applied to the structure design involves 1. growing complex tensile-strained ZnSe-1.5 nm/ZnS 0.15 Se 0.85 -3.5 nm/ZnSe-1.5 nm barriers between compressively strained QD sheets, which provide efficient tunnelling of non-equilibrium carriers [5], and 2. compensation of the compressive strain induced by the ZnMgSSe/ZnSe GIW SLs by intentionally reducing the average lattice parameter of the central flat-band ZnS 0.15 Se 0.85 /ZnSe waveguide SL below that of GaAs [6]. The high structural quality of the structure as well as good agreement of intended and as-grown SL period thicknesses are confirmed by the cross-section TEM image shown in Fig.…”

“…The laser chips with a short cavity length ( 100 mm) were employed to achieve a minimum threshold power value [5]. The maximum room temperature values of the pulse output power of P max ¼ 154 mW (l las ¼ 543 nm) and quantum conversion efficiency of h ¼ 25.4% have been achieved at the excitation level of P exc 1.0 W (l ex ¼ 416 nm) for the structure with five QD sheets in the active region placed in the asymmetrical GIW waveguide which provides better overlap of the active region with the fundamental light mode.…”

“…To realise the next generation of converters using blue-violet III-N LDs as pumping sources two essential obstacles should be overcome. First, the threshold power density of II-VI laser heterostructures has to be reduced via structure design and growth optimisation, and, secondly, high-power blue-violet III-N LDs or high-brightness LEDs should appear on the market, which, in turn, is governed by the progress in III-N LD technology.Recently, utilising II-VI laser heterostructures of conventional design [4], but containing five electronically coupled CdSe/ZnSe quantum dot (QD) planes instead of two, allowed us to achieve the pulse output power in green of 65 mW and the quantum conversion efficiency of 8% for the converter pumped by a commercial blue-violet LD (l exc ¼ 416 nm) [5]. The threshold pulse power in that case was 0.65-0.7 W. This Letter reports on the next step in the realisation of high-efficiency violet-togreen electrically pumped laser converters based on the optimised II-VI laser heterostructures with a superlattice (SL) graded-index waveguide (GIW), which demonstrated significantly reduced threshold power density P th 1.5 kW/cm 2 [6].…”

“…Recently, utilising II-VI laser heterostructures of conventional design [4], but containing five electronically coupled CdSe/ZnSe quantum dot (QD) planes instead of two, allowed us to achieve the pulse output power in green of 65 mW and the quantum conversion efficiency of 8% for the converter pumped by a commercial blue-violet LD (l exc ¼ 416 nm) [5]. The threshold pulse power in that case was 0.65-0.7 W. This Letter reports on the next step in the realisation of high-efficiency violet-togreen electrically pumped laser converters based on the optimised II-VI laser heterostructures with a superlattice (SL) graded-index waveguide (GIW), which demonstrated significantly reduced threshold power density P th 1.5 kW/cm 2 [6].…”