A new technique utilizing harmonic Fourier spectra created by the non-linear properties of a compact Fourier transform infrared interferometer (FTIR) was proposed and realized to improve the system resolution. The compact standing wave FTIR (SWFTIR) system consists of a partial transparent hetero-junction bipolar phototransistor (HPT) and a free scanning highly reflective mirror. The overall size of the system is less than 5×5×5cm3, and the resolution at 1.5μm is better than 37.5cm-1 at the 5th harmonic spectral component. The SWFTIR array system has theoretical resolution of better than 1cm-1 covering the whole near-infrared region with potential compact portable applications.
We have demonstrated all-epitaxially fabricated orientation-patterned AlGaAs waveguides with reduced waveguide core corrugation for the quasi-phase-matched second harmonic generation (SHG) pumped at 1.55 μm. The attenuation coefficient is measured to be ~4.5 dB/m at 1.55 μm, and ~9.7 dB/cm at 780 nm. The conversion efficiency at continuous wave operation is 43%W-1 with an 8-mm long waveguide.
Near-infrared detection has a lot of application in the fields of telecommunication, bio-sensing, environmental gas detection and hyper-spectral spectrometer. Phototransistor is one of the most promising photodetection devices that can provide integrated photo current gain even at high-speed operating conditions. A double heterojunction phototransistor was grown by molecular beam epitaxy (MBE) and fabricated on semi-insulating InP substrate. The collector-up device structure consists of InP emitter, InGaAs base, InAlAs collector and subcollector, InGaAs/InAlAs superlattice graded emitter-base (EB) and base-collector (BC) junctions. A solid GaP source was used to clean the InP substrate and grow InP buffer and emitter layer. In-situ Reflective High-Energy Electron Diffraction (RHEED) and ex-situ X-Ray Diffraction (XRD) were utilized to monitor the material growth for lattice match condition of InGaAs and InAlAs to InP substrate. A digital-alloy MBE growth technique was applied to implement the graded interfacial layers of EB junction and BC junction. The performance of the device was characterized, including current-voltage characteristics, breakdown and responsivity at the wavelength of 1.55um (telecommunication application). Simple model of phototransistor current gain with different device parameters and various operating conditions was developed and applied to the device design for hyper-spectral spectrometer application.
The dilute-nitride GaInNAs shows great promise in becoming the next choice for long-wavelength (0.9 to 1.6 μm) photodetector applications due to the ability for it to be grown lattice-matched on GaAs substrates. GaAs-based devices have several advantages over InP-based devices, such as substrate cost, convenience of processing, and optoelectronic band parameters. This paper will present results from the first high-quality thick GaInNAs films grown by solid state molecular beam epitaxy with a nitrogen plasma source and the first high efficiency photodetectors which have been fabricated from those materials. GaInNAs films up to 2 microns thick have been grown coherently on GaAs substrates. These films exhibit reasonable photoluminescence intensities at peak wavelengths of 1.22 to 1.13 μm before and after a rapid thermal anneal at a series of temperatures. PIN photodiodes with these thick GaInNAs films in the intrinsic regions show responsivity (better than 0.5 A/W at 1.064 μm), dark current (200 nA at -2 V), and signal-to-noise ratio (greater than 105) approaching those of commercially available InGaAs/InP devices. Furthermore, it will be shown that these devices show significantly lower dark current and higher signal-to-noise ratio than similar metamorphic InGaAs/GaAs structures.