High-power bipolar and unipolar quantum cascade lasers

High-power bipolar and unipolar quantum cascade lasers were designed, fabricated and characterized. The importance of lateral current spreading is emphasized since it plays an important role in operation of these devices.; Edge-emitting, gallium arsenide (GaAs) based bipolar cascade lasers were fabricated from metalorganic chemical vapor deposition-grown material containing two diode laser structures separated by a quantum-well tunnel junction (QWTJ). The QWTJ was comprised of a thin, high indium content indium gallium arsenide layer sandwiched between relatively low-doped, p-type and n-type GaAs layers. Comparison of near field data with predictions from a one dimensional current spreading model shows that this type of reverse-biased QWTJ has a low effective resistivity. As a consequence, current spreading perpendicular to the laser length in the plane of the layers (lateral direction) is reduced leading to a relatively low threshold current for the second stage. In addition, the differential quantum efficiency ∼150% of these double stage lasers is nearly twice that of single stage lasers.; Low-ridge unipolar quantum cascade lasers operating at 5.3mum were fabricated from InP-based MOCVD-grown material. Record-high maximum output pulsed optical power of 12W at 14A was measured from a low-ridge chip with a high reflectivity coated back facet at 80K. Also, Far-Field measurements demonstrated current beam steering for this device. Modeling shows that the lateral variation of transverse conductivity is essential for an accurate description of current spreading in these devices.