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 o C to above 150 o 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.

Modulation bandwidth of a double tunnelling-injection quantum dot laser

“…As an alternative to conventional pumping, tunnelling-injection of carriers into a low-dimensional active region of diode lasers was considered. In [1][2][3][4][5][6][7][8][9], single tunnelling-injection was proposed, which was tunnelling-injection of carriers of one type only (electrons) while the carriers of the opposite sign (holes) were injected conventionally, i.e., first injected into the optical confinement layer (OCL) and then captured into the active region. In [1], single tunnelling-injection was utilized into a two-dimensional (2D) active region (quantum well, QW), and in [2][3][4][5][6][7][8][9] into a zero-dimensional (0D) active region (quantum dots, QDs).…”

“…In [1][2][3][4][5][6][7][8][9], single tunnelling-injection was proposed, which was tunnelling-injection of carriers of one type only (electrons) while the carriers of the opposite sign (holes) were injected conventionally, i.e., first injected into the optical confinement layer (OCL) and then captured into the active region. In [1], single tunnelling-injection was utilized into a two-dimensional (2D) active region (quantum well, QW), and in [2][3][4][5][6][7][8][9] into a zero-dimensional (0D) active region (quantum dots, QDs). Double tunnelling-injection (DTI), i.e., tunnelling-injection of both electrons and holes into QDs was proposed in [10,11] and further studied theoretically in [12][13][14].…”