Abstract
Quantum cascade lasers (QCLs) that employ metamorphic buffer layers as substrates of variable lattice constant have been designed for emission in the 3.0- to 3.5-μm wavelength range. Theoretical analysis of the active-region (AR) energy band structure, while using an 8-band k•p model, reveals that one can achieve both effective carrier-leakage suppression as well as fast carrier extraction in QCL structures of relatively low strain. Significantly lower indium-content quantum wells (QWs) can be employed for the AR compared to QWs employed for conventional short-wavelength QCL structures grown on InP, which, in turn, is expected to eliminate carrier leakage to indirect-gap valleys (X, L). An analysis of thermo-optical characteristics for the complete device design indicates that high-Al-content AlInAs cladding layers are more effective for both optical confinement and thermal dissipation than InGaP cladding layers. An electroluminescence-spectrum full-width half-maximum linewidth of 54.6 meV is estimated from interface roughness scattering and, by considering both inelastic and elastic scattering, the threshold-current density for 3.39-μm-emitting, 3-mm-long back-facet-coated QCLs is projected to be 1.40 kA/cm2.
Highlights
High-power lasers operating in the mid-infrared (IR) spectral region with emission in the 3.0- to 3.5-μm wavelength range have garnered interest due to applications such as advanced remote sensing and ranging
High-performance, low threshold-current density, interband-transition lasers have been reported within the 3.0- to 3.5-μm wavelength range by employing either type-I quantum wells (QWs)[1,2,3] or typeII QWs.[4,5,6]
We have previously proposed the use of metamorphic buffer layers (MBLs) as the means to achieve highperformance low-strain Quantum cascade lasers (QCLs) at 3.0- to 3.5-μm emission wavelengths.[19,20]
Summary
High-power lasers operating in the mid-infrared (IR) spectral region with emission in the 3.0- to 3.5-μm wavelength range have garnered interest due to applications such as advanced remote sensing and ranging. Electron energy-state lifetimes have been calculated using an 8-band kp code, as previously reported.[19] Conventional QCL structures utilize fixed compositions for the wells and barriers with variations only in the thickness of each layer type For such QCLs, it has been found[11] that for 3.76-μm-emitting devices[23] one can achieve both efficient carrier-leakage suppression and fast, miniband-like carrier extraction when using, for lower-laser-level depopulation, the single-phonon-resonance (SPR) AR structure in conjunction with resonant-tunneling extraction from the lower laser level.[24] We have achieved the same type of AR design (i.e., SPR + miniband extraction) for our short-wavelength (λ 1⁄4 3.0 to 3.5 μm) QCL structures grown on MBLs. an SPR + miniband extraction AR design was reached given a lattice constant of 0.574 nm for the virtual substrate (i.e., the cap layer of the MBL) so as to provide a relatively low-strain QCL structure for emission in the 3.0- to 3.5-μm wavelength range.
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