O-band excited state quantum dot bilayer lasers

Abstract

Bilayer InAs/GaAs quantum dot (QD) lasers operating in the excited state at wavelengths that span the O-band are demonstrated. The higher saturated gain and lower scattering time of the excited states of the ensemble of QDs offers the opportunity for fast direct-modulation lasers. We predict an increase in K-factor limited modulation bandwidth from QD lasers operating in the excited state due to a reduction in carrier transport and scattering times whilst maintaining high peak modal gain. Semiconductor diode lasers incorporating self-assembled quantum dots (QDs) on GaAs substrates accessing the International Telecommunication Union (ITU) O-band (1.26-1.36 lm) have received considerable attention, to the point of their current commercialization, 1,2 with recent performance milestones reached including high-speed, temperature-insensitive 3 operation around room temperature (RT) at 1.3 lm through the use of p-type doping. 4 In contrast to quantum well lasers, the modulation dynamics of QD lasers are limited by damping, 5 and in order to achieve high modulation rates, low carrier scattering times into the lasing state and high saturated modal gains are required. Possible routes to increase saturated gain include careful optimization of growth conditions to increase QD areal density 6 or to increase differential gain by increasing p-doping, but this has practical limit in terms of additional loss. 7 It has recently been demonstrated that operation using the excited state (ES) of the QDs exhibit much higher damping limited bandwidths as compared to ground state (GS) lasers. 8,9 This enhancement was attributed to higher saturated gain (double) and lower scattering time (half) compared to the ground state. However, this is achieved at the expense of higher operating currents and shorter operating wavelengths that may be impractical for fiber-optic based optical communications applications.Here, we demonstrate that the technologies to realize long wavelength QD GS emission can be applied to realize QD ES emission spanning the O-band. In this paper, we report on the fabrication of QD bilayer 10,11 materials where ES lasing is demonstrated between 1.26 lm and 1.33 lm spanning the ITU O-band. This is achieved by using QD material comprising closely stacked layers of QDs, which are strain and electronically coupled, consisting of a seed layer that determines the areal density and an upper emission layer. The wavelength coverage is made possible by utilizing both GaAs and InGaAs capping of the emission layer. Measurement of multi-section lasers containing these QD bilayers allows the peak modal gain of the ES as a function of current density to be deduced, 12 and this is comparable to commercially available 1.3 lm QD laser samples operating in the GS.

Investigation of the InAs/GaAs Quantum Dots’ Size: Dependence on the Strain Reducing Layer’s Position

“…InAs self-assembled QDs formed by Stranski-Krastanov growth mode have been a subject of intense research activity towards the development of innovative devices such as QDs lasers [ 1 , 2 ], light emitters and detectors [ 3 , 4 , 5 , 6 ]. More recently, this kind of QDs has been found to be promising for photovoltaic applications [ 7 ].…”

Electronic and Optical Properties of InAs QDs Grown by MBE on InGaAs Metamorphic Buffer

“…To extend the spectral range of emission, it is necessary to apply additional steps to modify the properties of the dots, mostly employing the strain engineering or modification of the QDs’ size or composition [ 11 ]. There exist at least several approaches allowing for the shifting of the emission wavelength to the telecommunication windows, for instance by using vertically-stacked QDs [ 19 , 20 , 21 , 22 , 23 ], growth up to the second critical thickness [ 24 , 25 ], controlled overgrowth of InGaAs QDs [ 26 ], adding small concentrations of nitrogen to the InAs QDs [ 27 ], applying the strain-reducing layer [ 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 ], or the metamorphic-buffer-layer (MBL) [ 5 , 11 , 43 , 44 , 45 , 46 ]. Most of these solutions concern the use of QDs as an active region in lasers or amplifiers, while the practical demonstrations employing single GaAs-based QDs as an active element of non-classical emitters for quantum technology applications in the telecom range are still under development.…”

Effects of a thin nitrogen-doped layer on terahertz dynamics in GaAs containing InAs quantum dots

“…Control of the optical properties of self-assembled quantum dots (QDs) is essential for device applications such as in lasers [1][2][3], single photon sources [4][5][6], and solar cells [7][8][9]. The control of strain [10][11][12] and intermixing of Ga and In [13][14][15] in case of InAs QDs on GaAs have been reported as methods to control the QD characteristics.…”