The characteristics of intersubband transitions in III-nitride quantum wells are promising for detectors and all-optical
switches through a high intrinsic speed (~1 THz), and can also provide a high optical saturation power and a desired
small negative chirp parameter in electroabsorption modulators. The high LO-phonon energy allows to improve the
operating temperature of THz emitters. Recent achievements and prospects for intersubband III-nitride photonic devices,
mainly for λ=1.55 μm, are briefly reviewed. Further, means to enhance material quality by achieving crack-free growth
of GaN/AlN multiple-quantum-well (MQW) structures, and by employing intersubband transitions in multiple-quantum-disk
(MQD) structures incorporated into dislocation free GaN nanocolumns are discussed. We investigate the occurrence
of cracks in MBE-grown GaN/AlN MQWs on GaN MOVPE templates with respect to the buffer layer, the number of
QWs and the temperature reduction rate after growth. Intersubband absorption in GaN/AlN MQDs in the wavelength
range 1.38-1.72 μm is demonstrated in three samples grown on Si(111).
We have used MBE to grow MQW structures on MOVPE GaN/sapphire templates. The MQW devices are intended for high speed intersubband electroabsorption modulator devices operating at 1.55-&mgr;m. The GaN/AlN multiple quantum well material was systematically studied regarding the surface morphology, structural characterization and optical property by atomic force microscopy, X-ray diffraction and Fourier transform infrared spectroscopy, respectively. The intersubband resonance energy was also calculated considering many-body effects in n-type doped structures. The multiple quantum well structure showed superior performance in terms of linewidth when grown on GaN templates as compared on sapphire. GaN quantum well and AlN barriers with a thickness of 3.3 and 4.2 nm respectively resulted in FWHM of the intersubband absorption peak as low as 93 meV at an absorption energy of 700 meV. This is promising for intersubband modulator applications.
In this work we present performance characteristics of metalorganic vapor-plase epitaxy grown GaInNAs and InGaAs quantum-well (QW) vertical-cavity lasers (VCLs) for 1.3-μm applications. The InGaAs VCLs emit in a wavelength range from 1200 to somewhat above 1260 nm, while the GaInNAs VCLs operate from 1264 to 1303 nm. The InGaAs VCLs are based on highly strained InGaAs double QWs, with photoluminescence (PL) maximum around 1190 nm, and extensive negative gain-cavity detuning. As a consequence, these devices are strongly temperature sensitive and the minimum threshold current is found at very high temperature (~90-100°C). Both kind of VCLs work continuous-wave well above 100°C, and while the InGaAs VCLs reach slightly higher light output power, they show significantly larger threshold currents. In addition, the large device detuning also has profound effects on the high-frequency response. Nevertheless, for a 1260-nm device, 10 Gb/s transmission is demonstrated in a back-to-back configuration. We also show that by further optimization of the InGaAs QWs the PL peak wavelength can be extended to at least 1240 nm. The incorporation of such QWs in the present VCL structure should considerably improve the device performance, resulting in higher light output power, lower threshold current, and reduced temperature sensitivity with a shift of the minimum threshold current towards room temperature, thus approaching standard VCL tuning.
We compare GaInNAs and highly strained InGaAs quantum-wells (QWs) for applications in metal-organic vapor-phase epitaxy (MOVPE)-grown GaAs-based 1300-nm vertical-cavity lasers (VCLs). While the peak wavelength of InGaAs QWs can be extended by a small fraction of N, the luminescence efficiency degrades strongly with wavelength. On the other hand, using highly strained InGaAs QWs in combination with a large VCL detuning it is also possible to push the emission wavelength towards 1.3 μm. The optimized MOVPE growth conditions for such QW and VCL structures are discussed in some detail. It is noted that GaInNAs and InGaAs QWs preferably are grown at low temperature, but with quite different V/III ratios and growth rates. We also point out the importance of reduced doping concentration and growth temperature of the n-doped bottom DBR to minimize optical loss and for compatibility with GaInNAs QWs. InGaAs VCLs with emission wavelength beyond 1260 nm is demonstrated. This includes mW-range output power, mA-range threshold current and 10 Gb/s data transmission.
As the bit rates of high-speed data transmission increase, the dynamic properties of the VCSEL are becoming more important. High photon density is of great importance for high modulation efficiency and low noise. We will present a schematic of the Zarlink 850nm 10Gb/s selectively oxidized VCSEL design and results from small and large signal modulation. The modulation characteristics were improved by utilizing InGaAs quantum wells, which have better gain characteristics than GaAs wells. 10Gb/s transmission over 300m of OFS-Fitel LaserWavetm 300 Fiber for a 12micrometers aperture multimode VCSEL at 80 degree(s)C will be demonstrated. Bit error rate (BER) measurement with the corresponding power penalty will also be presented.
For high speed data communication, Zarlink has developed GaAs PIN detectors with three different diameters of the apertures: 40 micrometers , 55 micrometers and 70 micrometers . To minimize the capacitance we have chosen to use a mesa structure on a semi-insulating substrate. At íV2 Volt bias the capacitances are 110 fF, 160 fF and 230 fF for the 40 micrometers , 55 micrometers and 70 micrometers detectors respectively. For all diameters the series resistance is about 5 (Omega) and the responsivities are 0.6 A/W. At-V10 Volt bias, the dark current is less than 100 pA. Link experiments show open eye diagrams at 10 Gbit/s for a 70 micrometers unamplified PIN detector, both at room temperature and at 90 degree(s)C.
We present an approach for systematic high-speed characterization of VCSELs and discuss both its potential benefits and problems. We show how the VCSEL dynamics, under certain conditions, can be well described by a small number of key parameters that can be extracted from measurements and used for further optimization. The calibrated small signal modulation responses of the laser are measured and fitted to an analytical transfer function allowing the estimation of the resonance frequency, damping factor and parasitic cut-off at different bias points. From this data the relative importance of different bandwidth limiting effects due to damping, thermal heating and parasitics can be deducted. We illustrate the approach on 850nm datacom VCSELs using either ion implantation, selective oxidation or semi-insulating regrowth for current confinement. The bandwidth ofthe implanted device appears to be limited by parasitics effects to 3.3GHz. Due to a much smaller injection diameter, the oxidized VCSEL reaches 10GHz, being mainly limited by the high damping. Finally the regrown VCSEL operates up to 5GHz, limited by the parasitics
MITEL Semiconductor is developing the next generation low cost, high performance transceivers for data communication. The increasing quantity of data being transferred over the Internet demands very high capacity interconnects. A low cost, high-performance alternative is the use of parallel fiber interconnects where the light is, for example, coupled into a 12channel fiber-ribbon. Parallel interconnects require good uniformity in order to reduce escalating costs and complexity. In this paper we report on the static and the modulation properties of 850nm multimode oxide VCSELs for use in such Gb/s transceiver system. Static power-current-voltage characteristics with good uniformity were obtained for different structures, with threshold currents down to sub-mA. A maximum small signal 3-dB bandwidth of 10 GHz and a modulation current efficiency up to 8.4 GHztsJ[rnA] were measured. Single channel results are presented for VCSELs operated at data rates from 2.5-10Gb/s.
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