Molecular Beam Epitaxy Growth for Quantum Cascade Lasers

Abstract

The fabrication of quantum cascade lasers emitting at 9 µm is reported. The devices operated in pulsed mode at up to 260 K. The peak powers recorded at 77 K were over 1 W and the slope efficiency η ≈ 0.5-0.6 W/A per uncoated facet. This has been achieved by the use of GaAs/Al0.45Ga0.55As heterostructure, with the "anticrossed-diagonal" design. Double plasmon planar confinement with Al-free waveguide has been used to minimize absorption losses. The double trench lasers were fabricated using standard processing technology, i.e., wet etching and Si3N4 for electrical insulation. The quantum cascade laser structures have been grown by molecular beam epitaxy, with Riber Compact 21 T reactor. The stringent requirements -placed particularly on the epitaxial technology -and the influence of technological conditions on the device structure properties were presented and discussed in depth.

Multi-step interrupted-growth MBE technology for GaAs/AlGaAs (∼9.4 μm) room temperature operating quantum-cascade lasers

“…The above mentioned calculations were done at the electrical field of 48 kV/cm close to an esti− mated laser threshold. The active region doping was applied for only two barrier−QW pairs in the central part of each in− jector; it has been tested by us in the range of n i 0.4 -2.2×10 12 cm −2 per period [5,9]. The double−plasmon low− −loss Al−free waveguide was used for planar optical confinement [15].…”

“…There is a wide agreement that changes of the injector doping level in the range of few ten per cents are crucial [1,[4][5][6][7][8][9], though variations of about 10% may be acceptable [2,10].…”

Room temperature AlGaAs/GaAs quantum cascade lasers

“…The electronic band structure of QCL, calculated by solving the Schrödinger equation with position dependent ) GaAs layers. The details of the technology are given in earlier papers [5][6][7]. * effective mass is shown in Fig.1.…”

“…After the wafer was thinned down to about 100µm, an alloyed AuGe/Ni/Au contact was deposited on the backside. The lasers were cleaved into bars of 1, 1.5 and 2mm length and the soldered epilayer down on copper submounts [6]. We have used indium soldering or direct Au/Au bonding.…”

“…The waveguide losses estimated by measuring devices with a different resonator length, fabricated from the same epitaxial wafer, are of the order of 30cm -1 . The threshold current density can be calculated from the equation [6] where the injection efficiency of unity in the upper laser level E3 is assumed and direct tunnelling processes out of levels E2 and E3 are neglected. In this equation, ε 0 is the vacuum permittivity, n is the effective refractive index of the laser mode, λ is the emission wavelength, L p is the length of one segment, γ 32 is the full width at the half maximum (FWHM) of the spontaneous emission spectrum, e is the electron charge, Γ is the confinement factor and z 32 is the matrix element of the laser transition.…”