AlAs/GaAs quantum cascade lasers based on large direct conduction band discontinuity

Abstract

The design and operation of quantum cascade (QC) lasers using AlAs/GaAs coupled quantum wells are reported. In this material system, the conduction band offset at the Γ point (∼1 eV) is much higher than in previously reported QC lasers. The use of high band discontinuity allows us to increase the energy separation among the subbands, thus suppressing thermally activated processes which limit device performance at high temperature. The measured thermal characteristics of these promising devices are strongly improved from previously reported GaAs-based QC lasers: The temperature dependence of the threshold current density is described by a very large T0 (320 K) and the laser slope efficiency does not vary for increasing heat sink temperatures. The maximum operating temperature is 230 K, limited by negative differential resistance effects that occur when the applied bias reaches 8 V.

Self-consistent scattering theory of transport and output characteristics of quantum cascade lasers

“…The main reason was the fact that a large amount of experimental results have been published 5,10,11,30 for the structure. Having demonstrated the capability of the model by comparison with this experimental data, it may be readily extended to analyze recent improved designs, [7][8][9][10][11] and to optimize the design of structures. The layer sequence of one injector-active region period of structure, in nanometers, from left to right starting from the injection barrier is 5.8/1.5/ 2.0/4.9/1.7/4.0/3.4/3.2/2.0/2.8/2.3/2.3/2.5/2.3/2.5/2.1, where the normal script are wells and bold script barriers.…”

“…6 The midinfrared GaAs/AlGaAs QCLs have not yet achieved the temperature range of InGaAs/AlInAs devices, but a lot of successful experimental work is currently under way to extend the operating temperature. [7][8][9][10][11][12][13] On the other hand, GaAs/ AlGaAs cascade structures may play an important role in producing stimulated radiation in the far-infrared region, which is also the topic of recent investigations, both experimental 14 -16 and theoretical. 17,18 The rapid experimental development has stimulated interest in theoretical work to explain the physical processes involved, [19][20][21] including the principles of carrier transport in devices, and hence, indicate routes to optimized layer design for improved output characteristics.…”

GaAs Quantum Cascade Lasers: Fundamentals and Performance

“…10). Both these approaches have shown significant improvements of the thermal behaviour of our lasers, and will be discussed in details in the following two sections [29,32]. …”

Midinfrared intersubband absorption in strain-compensated InGaP/InGaAs superlattices on (001) GaAs

“…3,4 The maximum conduction band edge offset ⌬E c between direct band gap AlGaAs and GaAs is about 340-390 meV, 5,6 large enough to allow emission wavelengths in QCLs as short as 9 m. 6 Using strained InGaAs in the wells further increases ⌬E c and extends the emission wavelength range to 7.4 m. 7 The use of indirect band gap AlGaAs including AlAs, however, does not appreciably increase the maximum emission energy. 8 An alternative material system which is also lattice matched to GaAs is the strain-compensated ͑In,Ga͒P/ ͑In,Ga͒As system, 9 the strain-compensated extension of In 0.49 Ga 0.51 P/GaAs. Although ⌬E c in the lattice-matched In 0.49 Ga 0.51 P/GaAs system is too small to use for midinfrared QCL applications, the model-solid theory of Van de Walle 10 predicts a ⌬E c of 480 meV for In 0.32 Ga 0.68 P/In 0.32 Ga 0.68 As, a combination where both materials can be epitaxial deposited and are direct band gap.…”