Abstract
Electrically pumped AlSb/InAs-based quantum cascade (QC) devices have already shown well resolved peaks of luminescence in the 3-5 μm range.1 To obtain a laser, cladding layers have to be added to the structure, in order to maximize the overlap of the emitted radiation with the active region. To this end, we use a 20 Å/20 Å InAs/AlSb superlattice where the InAs layers are n doped with Si n = 5 × 1018 cm−3. This type of cladding has already been used in interband cascade lasers.2 For an active region at ~4 pm made of AlSb/InAs, the InAs content is approximately 66%. in this case, the contrast of the refractive indices between the waveguide core and the cladding is very small. (3.4 in the active region and 3.35 in the claddings, where we used nInAs=3.5 and nAlsb) = 3.2). To overcome this problem, we have designed an active region where we have introduced undoped GaSb layers. By doing so, we take advantage of the high refractive index of GaSb (nGaSb = 3.74) to increase that of the waveguide core. In this active region, the barriers are composed of a thin layer of AlSb (~ 2 monolayers) sandwiched between two GaSb layers. The resulting potential profile is shown in Fig. 1, where we present the schematic conduction band diagram as well as the moduli squared of the most relevant wavefunctions of such a structure. The latter is based on a bound-to-continuum design where the transition occurs between a distributed bound upper state and a lower miniband [Ref. 3] (sec Fig. 1).
© 2002 Optical Society of America
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