Results of detector characterization are presented for quantum well infrared photodetectors (QWIPs) fabricated from a variety of III-V material systems lattice-matched to InP substrate. Extremely large responsivities of 33.2 A/W were obtained from GaInAs/InP QWIPs operating at (lambda) equals 9 micrometers which represents to the authors' knowledge the largest value of responsivity for any QWIP in this wavelength range. Devices made from AlGaInAs/InP and GaInAs/AlInAs have also been realized that extend the wavelength range of sensitivity from 3 micrometers out to 20 micrometers while remaining lattice-matched to InP. Lattice-matched multispectral detectors are demonstrated for sensitivity at both 4 micrometers and 8.5 micrometers . Localized epitaxy of GaInAs/InP superlattice structures lattice-matched to InP was performed on Si substrate for the purpose of monolithic integration of III-V QWIPs with Si-based readout integrated circuitry.
There is currently a strong interest in developing solid- state, UV photodetectors for a variety of applications. Some of these are early missile threat warning, covet space to space communications, flame monitoring, UV radiation monitoring and chemical/biological reagent detection. The III-Nitride material system is an excellent candidate for such applications due to its wide, reagent detection. The III-Nitride material system is an excellent candidate for such applications due to its wide, direct bandgaps and robust material nature. However, despite many inherent material advantages, the III-Nitride material system typically suffers from a large number of extended defects which degrade material quality and device performance. One technique aimed at reducing defect densities in these materials is lateral epitaxial overgrowth (LEO). In this work, we present a preliminary comparison between AlGaN UV, solar-blind p-i-n photodiodes fabricated form LEO GaN and non-LEO GaN. Improvements in both responsivity and rejection ratio are observed, however, further device improvements are necessary. For these, we focus on the optimization of the p- i-n structure and a reduction in contact resistivity to p- GaN and p-AlGaN layers. By improving the structure of the device, GaN p-i-n photodiodes were fabricated and demonstrate 86 percent internal quantum efficiency at 362 nm and a peak to visible rejection ratio of 105. Contact treatments have reduced the contact resistivity to p-GaN and p-AlGaN by over one order of magnitude form our previous results.
We report the lateral epitaxial overgrowth (LEO) of GaN films on (00.1) Al2O3 and (111) Si substrates by metalorganic chemical vapor deposition. The LEO on Si substrates was possible after achieving quasi monocrystalline GaN template films on (111) Si substrates. X-ray diffraction, photoluminescence, scanning electron microscopy and atomic force microscopy were used to assess the quality of the LEO films. Lateral growth rates more than 5 times as high as vertical growth rates were achieved for both LEO growths of GaN on sapphire and silicon substrates.
We report the growth and characterization of Schottky based metal-semiconductor-metal ultraviolet photodetectors fabricated on lateral epitaxially overgrown GaN films. The lateral epitaxial overgrowth of GaN was carried out on basal plane sapphire substrates by low pressure metalorganic chemical vapor deposition and exhibited lateral growth rates more than 5 times as high as vertical growth rates. The spectral responsivity, the dependence on bias voltage, on incident optical power, and the time response of these photodetectors have been characterized. Two detector orientations were investigated: one with the interdigitated finger pattern parallel and the other perpendicular to the underlying SiOx mask stripes.
We report the fabrication and characterization of AlxGa1-xN p-i-n photodiodes (0.05 less than or equal to X less than or equal to 0.30) grown on sapphire by low-pressure metalorganic chemical vapor deposition. The devices present a visible-rejection of about four orders of magnitude with a cutoff wavelength that shifts from 350 nm to 291 nm. They also exhibit a constant responsivity for five decades (30 mW/m2 to 1 kW/m2) of optical power density. Using capacitance measurements, the values for the acceptor concentration in the p-AlxGa1-xN region and the unintentional donor concentration in the intrinsic region are found. Photocurrent decays are exponential for high load resistances, with a time constant that corresponds to the RC product of the system. For low load resistances the transient response becomes non- exponential, with a decay time longer than the RC constant.
980 nm GaInAs/GaAs/GaInP separate-confinement heterostructure single quantum well lasers are fabricated by LP-MOCVD. The lasers exhibit threshold current density of 170 A/cm2, output light power 2W in continuous wave, slope efficiencies of 0.91 W/A without mirror coating. The characteristic temperature T0 is 330 degree(s)K.
Continuous-wave (CW) room temperature operation of InGaN/GaN multi-quantum well (MQW) lasers is reported. Far-field beam divergence as narrow as 13 degrees and 20 degrees for parallel and perpendicular directions to epilayer planes were measured, respectively. The MQW lasers showed strong beam polarization anisotropy as consistent with QW laser gain theory. Dependencies of threshold current on cavity-length and temperature are also consistent with conventional laser theory. No significant degradation in laser characteristics was observed during lifetime testing for over 140 hours of CW room temperature operation.
In this work, we present our recent achievements for the reliability of the Al-free lasers at high temperatures and high powers. Laser operations up to 30,000 hours were achieved without any degradation in the lasers characteristics from 7 randomly selected InGaAsP/GaAs diodes for (lambda) equals 808 nm. The test were performed for lasers without mirror-coating for optical power of 0.5 to 1 W CW at 50 approximately 60 degree(s)C. To the best of our knowledge, this is the first direct demonstration of the extremely high reliability of Al-free diodes operations at high powers and temperatures for periods of time much longer than practical need (approximately 3 years). The characteristics during the tests are discussed in detail.
We report metalorganic chemical vapor deposition-grown double heterostructure and multiple quantum well InAsSb/InAsSbP laser diodes emitting at 3 to 4 micrometers and light emitting diodes up to 5 micrometers . Maximum output power up to 1 W was obtained from a MQW laser with stripe width of 100 micrometers and cavity length of 700 micrometers for emitting wavelength of 3.6 micrometers at 90 K. Maximum operating temperature up to 220 K with threshold current density of 40 A/cm2 at 78K were achieved from the double- heterostructure lasers emitting at 3.2 micrometers . The far-field beam divergence as narrow as 24 degrees was achieved with the sue of higher energy gap barrier layers, i.e., lower effective refractive index, in MQW active region. We also discuss the effect of composition-fluctuation in the InAsSb active region on the gain and threshold current of the lasers.
The operating characteristics of Al-free InGaAsP/GaAs separate confinement heterostructure single quantum well high power laser grown by low-pressure metalorganic chemical vapor deposition are reported. The internal differential quantum efficiency (eta) i is closed 98 percent. The external differential quantum efficiency (eta) d of 75 percent and characteristics temperature To of 146 degrees C are achieved, CW total output power both facets of 2.6 W single quantum well laser with 100 micrometers width, 1.1 mm cavity length is obtained. Threshold current density Jth, reciprocal differential quantum efficiency l/(eta) d, emission wavelength (lambda) and characteristics temperature To as function of laser cavity length L respectively have been measured and researched. Dependence of Jth (T), (lambda) (T), and (eta) d (T) respectively on temperature T have been given and explained.
In this paper, we studied the effects of the active region structure (one, two and three quantum wells with same total thickness) for high-power InGaAsP-GaAs separate confinement heterostructure lasers emitting at 0.8 micrometers wavelength. Experimental results for the lasers grown by low pressure metalorganic chemical vapor deposition show excellent agreement with the theoretical model. Total output power of 47 W from an uncoated 1 cm-wide laser bar was achieved in quasi-continuous wave operation.
GaInAsP lattice matched to GaAs in the entire bandgap range has been grown by low-pressure metalorganic chemical vapor deposition. Small mismatch and strong interference fringes in the x-ray spectrum, sharp photoluminescence (PL) peak, and high electron mobility indicate good control of the quaternary compositions, smooth epilayer interfaces, and coherent growth of the epilayers. Temperature coefficient of bandgap is measured from the temperature dependence of the PL peak to be 4.09 XT 10-4eV/K at 300K. Anomalous temperature dependence of PL at low temperature, similar to that reported for GaInP, is reported for GaInAsP/GaAs for the first time. It questions the attribution of the uncommon behavior to the crystal defects related to the long-range ordered structure.
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