Research Activities of the Integrated Photonic Devices and Materials Group

Long Wavelength Antimony-Based Devices

Figure 1) Compilation of PL spectra from numerous laser structures.

Figure 2) Optical power spectrum of a laser with two strained InGaAs quantum wells.

Figure 3) Continuous wave L-I-V curve at room temperature for the laser with two strained InGaAs quantum wells.
A mid-infrared (Mid-IR) semiconductor laser device is of great importance in terms of use in ultra sensitive molecular sensing applications, since several crucial toxic gas molecules (CH4, CO2, CO, and HCl) have their fundamental absorption lines within the spectral region spanning from 2 to 4 micron. Mid-IR laser diodes, operating at room temperature and emitting tens of milliwatts of power, can be designed in two major material systems: the antimonide-based material system and arsenide-phosphide-based material system. Sb-based devices can be designed to be nearly lattice-matched to GaSb, while the arsenide-phosphide-based devices emit around 2 micron if more than 1.5% of strain is incorporated in the quantum wells (QWs). In this work, a series of aluminum-cladded, phosphide-based laser structures with strained InGaAs quantum wells were grown and characterized. The laser structures were characterized by high resolution X-ray diffraction, photoluminescence (PL), and electroluminescence (EL). The light-current (L-I) and thermal resistance characteristics on ridge waveguide lasers were also measured.

The laser structures were composed of strained InGaAs QWs with barriers of In0.48Ga0.42Al0.1As and that are sandwiched between In0.48Ga0.42Al0.1As waveguide layers. InP acts as the cladding layers in these separate confinement heterostructures. Figure 1 shows that the PL emission wavelength increases from 1790 nm to 1970 nm with increasing indium, or equivalently strain, in the QWs.

For the laser that emitted at 1966nm, Figure 2 shows the continuous-wave room temperature optical spectrum while Figure 3 shows the L-I-V curve. The maximum output power of this laser was 10 mW. The internal loss and current injection efficiency were calculated to be 44.3 cm-1 and 67.4%, respectively from 1.0mm and 1.5mm long devices. The laser was driven by a continuous current source and was mounted epi-side down to minimize heating effects. This 1.97 micron emitting laser is being mounted in a butterfly package with a fiber pig-tail, to allow the laser to be used in a photo-acoustic spectroscopy cell for petrochemical trace gas sensing.

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