Modulation and thermal properties of tunnel-coupled InAs QD 1.13μm VCSELs

Abstract

Quantum dot (QD) -based vertical cavity surface emitting lasers (VCSELs) are predicted to have faster modulation response and better thermal stability as compared with quantum well (QW) VCSELs. QD size distribution, limited carrier capture and thermalization rates affect the maximum saturated gain of QD-based lasers. To address these problems, structures of tunnel coupled pairs consisting of InGaAs QW grown on top of self-assembled InAs QDs (QWon- QDs) were employed as a gain medium for VCSELs. Photoluminescence and transmission electron microscopy were used to study the properties of the "well-on-dots" active medium. We have developed a triple-pair tunnel QW-on-QDs structure with a QD transition which is red-shifted ~ 32 meV relative to QW ground state (GS). This optimized energy separation ▵E = E_QW - E_QDs was found to be close to the energy of the LO phonon. All-epitaxial tunnel-coupled QD VCSELs demonstrated continuous wave (CW) mode lasing in a wide temperature range from T = - 20°C to above 150°C. The room temperature lasing wavelength λ = 1131 nm corresponds to the QD GS transition. A minimum threshold current value I_th = 0.7 mA was measured in a 9 μm oxide aperture VCSEL. The maximum power from a single device was 2.5 mW and maximum differential efficiency was 0.16 W/A. Small signal modulation responses of these VCSELs showed a maximum resonance frequency of about 9 GHz. The damping-limited cut-off frequency for these tunnel QW-on-QDs VCSELs was estimated at 34 GHz from the dependence of damping factor and resonance frequency on driving current.