Abstract
Vertical cavity surface emitting lasers (VCSELs) are particularly well suited for Tunable Diode Laser Spectroscopy due to their intrinsic characteristics. Indeed, the low threshold single frequency emission producing a circular low divergence output beam is beneficial for the development of compact and low power consumption systems for gas spectroscopy. However, in the 3-4 μm range, which encompasses strong absorption bands of many species, only one VCSEL operating at room temperature (RT) in continuous wave mode (CW) have been reported so far. Towards the demonstration a VCSEL operating in the CW regime above RT, we propose a new alternative. This approach is based on Interband Cascade (IC) design for the active region, an arsenide oxide lateral confinement schema, a hybrid-mirror technology and on an intracavity contact.To provide efficient emission in the 3-4 μm range, the active region is based on a Sb-based IC type-II “W” QW structure. Principal characteristics of Sb-based QW lasers, such as the emission wavelength and threshold, are strongly affected by the growth temperature of the layers located above the active region. Using the optimized growth conditions, we succeeded to fabricate ICLs emitting at 3.3 μm and operating in the CW regime up to 80°C, which confirms the potential of the developed active region.Since the DBRs thickness scales with the wavelength, we employed a hybrid VCSEL configuration with a semiconductor AlAsSb/GaSb DBR in the bottom part of the device and a dielectric ZnS/Ge DBR on the top. Another issue in the VCSEL design is the high electrical resistance of the AlAsSb/GaSb DBR resulting in the overheating of the device. To reduce the ohmic losses we employed an intracavity injection scheme. Afterwards, to ensure an efficient lateral electro-optical confinement, we propose to use an oxide-aperture similarly as short infrared VCSELs. This approach is based on the metamorphic growth and the selective thermal oxidation of an Al(Ga)As heterostructure on top of a GaSb-based half-VCSEL. This architecture presents several advantages, and in particular the use of the well-controlled Al(Ga)As oxidation process.Finally, several vertical emitting structures as IC-LEDs, RC-LEDs and VCSELs were presented validating the assembly of the different parts previously studied.