Junxian Fu

Thick lattice-matched GaInNAs films in photodetector applications

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.

Solid-source molecular-beam epitaxy growth of GaInNAsSb/InGaAs single quantum well on InP with photoluminescence peak wavelength at 2.04 μm

Single quantum wells In0.53Ga0.47As/Ga0.47In0.53N0.021As0.949Sb0.03/In0.53Ga0.47As with room-temperature photoluminescence peak wavelength at 2.04 μm were grown on InP substrate by solid-source molecular-beam epitaxy (MBE). In situ reflection high-energy electron diffraction was used to monitor the MBE growth. Double-crystal high-resolution x-ray diffraction and secondary ion mass spectrometry were utilized to characterize the samples and optimize the growth conditions. The roles of nitrogen and antimony atoms in the growth of quinary material, GaInNAsSb, were investigated.

Widely tunable Al/sub 2/O/sub 3/-GaAs DBR filters with variable tuning characteristics

We demonstrate an optical tunable filter using Al/sub 2/O/sub 3/-GaAs layers as the top distributed Bragg reflector mirror. The mechanical properties and spectral response versus voltage are characterized. The tuning characteristics can be changed by removing the tensile-stressed Si/sub 3/N/sub 4/ on the mirror and legs. An integrated optical-mechanical model is used to analyze the result. Axial nitride and initial residual stress are incorporated into the model to obtain accurate fit. A 64-nm tuning range with 12-V tuning voltage is measured, a significant improvement over previous designs.

MBE grown GaInNAs solar cells for multijunction applications

Triple-junction cells composed of III-V materials currently hold the world record for photovoltaic efficiency. In order to further increase cell efficiency in the future 4- and 5-junction cells incorporating a sub-cell with a bandgap of roughly 1.0 eV will be required. In this study 1.0 eV bandgap GaInNAs devices grown by solid source molecular beam epitaxy are investigated in terms of materials quality and device performance that show similar or better properties to the best MOVPE grown devices found in the literature. Deep-level transient spectroscopy measurements illustrate that the trap concentrations in the GaInNAs material are significantly lower than that of MOVPE grown material. The internal quantum efficiency (43%), open-circuit voltage (450 mV), short-circuit current density (25.76 mA/cm/sup 2/) and fill-factor (56.4%) of the GaInNAs devices under 1-sun power density 1064 nm radiation are similar to or surpass the properties of the best MOVPE GaInNAs devices found in the literature.

Integrated standing-wave transform spectrometer for near infrared optical analysis

We have presented an integrated standing-wave spectrometer operating in the near a mirror flexure uniformity allows for increased mirror scan length without tip-tilt problems, which improves spectral resolution. The GaAs detector provides excellent near IR responsivity. The integrated design allows the mirror to move within a few gm of the detector. The simple operation of this compact device, with a low power continuous-scan mirror, permanent alignment, and only three contacts, should enable implementation in a wide variety of miniaturized sensing systems.

Design and Analysis of CMOS-Controlled Tunable Photodetectors for Multiwavelength Discrimination

In this paper, a metal-semiconductor-metal (MSM) based photodetector for multiple wavelength discrimination is fully introduced and analyzed. Its spectral response is programmable electrically through a set of low-voltage binary patterns that can be generated from CMOS circuits. Consequently, the wavelength reconfiguration time of the detector is set primarily by the electronics switching time, which is on the order of nanoseconds. Additionally, the spectral response of the detector can be arbitrarily shaped for any specific system need based on algorithms we introduce here. The nanosecond wavelength reconfigurability feature of the detector offers flexibility for designing high-efficiency wavelength reconfigurable optical networks.

Spectral shaping of electrically controlled MSM-based tunable photodetectors

Spectral shaping of electrically controlled metal-semiconductor-metal-based tunable photodetectors is experimentally demonstrated in the telecommunication C-band. By illuminating the device with more interference patterns, we can shape and design the spectral response of the detector for various system applications. The experimental results are in excellent agreement with the mathematical models.

Low loss orientation-patterned AlGaAs waveguides for quasi phase matched second harmonic generation

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.

Standing-wave Fourier transform interferometer with an HPT

A compact standing-wave Fourier transform interferometer is experimentally demonstrated in a very broad band. By using an InP-InGaAs-InAlAs heterojunction bipolar phototransistor (HPT) and a PZT-controlled scan mirror, a resolution of 37.5cm/sup -1/ was achieved with a mirror travel length of only 32/spl mu/m at the fifth harmonic order spectrum component. The experimental results agree well with the mathematical models, and the interferometer resolution could be further improved.

Compact standing-wave Fourier-transform interferometer with harmonic spectral analysis

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.