GaInAs/InP quantum well IR photodetectors (QWIP) were grown on Si substrate by metalorganic chemical vapor deposition. The growth condition of InP buffer layer on Si was optimized and its crystal quality was evaluated by high-resolution x- ray diffraction and atomic force microscopy experiments. Two different in-situ thermal cyclic annealing techniques were used to reduce the threading dislocation density in the InP- on-Si. The new thermal annealing with larger temperature range was found to improve the quality of InP-on-Si dramatically. QWIP-on-Si samples with these two different thermal annealing were prepared. Important detector properties, like dark current, spectral response, peak responsivity, and specific detectivity were studied and compared with a QWIP-on-InP sample with identical structure. Small blue shift was observed in both QWIP-on-Si detector's spectral responses. Record high detectivity of 2.3 X 109 cmHz/W was obtained for one QWIP-on-Si detector at 77K.
Quantum dots are recognized as very promising candidates for the fabrication of intersubband photodetectors in the infrared spectral range. At present, material quality is making rapid progress and some devices have been demonstrated. Examples of mid-infrared quantum dot intersubband photodetectors are presented along with device design and data analysis. Nonetheless, the performance of these devices remains less than comparable quantum well intersubband photodetectors due to difficulties in controlling the quantum dot size and distribution during epitaxy.
There has been a growing interest for the development of solar blind ultraviolet (UV) photodetectors for use in a variety of applications, including early missile threat warning, flame monitoring, UV radiation monitoring and chemical/biological reagent detection. The AlxGa1-xN material system has emerged as the most promising approach for such devices. However, the control of the material quality and the device technology are still rather immature. We report here the metalorganic chemical vapor deposition, the n-type and the p-type doping of high quality AlxGa1-xN thin films on sapphire substrates over a wide range of Al concentration. The quality of this AlxGa1-xN material was verified through the demonstration of high performance visible and solar blind ultraviolet p-i-n photodiodes with a cut-off wavelength continuously tunable from 227 to 365 nm, internal quantum efficiencies up to 86% when operated in photovoltaic mode, and a ultraviolet-to-visible rejection ratio as high as six orders of magnitude. Both front and back side illuminated p-i-n photodiodes were realized. Photodetector devices were also demonstrated on GaN material obtained using lateral epitaxial overgrowth. The technology for such AlxGa1-xN based devices was improved in an effort to enhance their performance, including the development of ohmic metal contacts to both n-type and p-type AlxGa1-xN films with an Al concentration up to 40%.
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.
Multi-quantum well structures of GaxIn1-xAsyP1-y were grown by metalorganic chemical vapor deposition for the fabrication of quantum well IR photodetectors. The thickness and composition of the wells was determined by high-resolution x-ray diffraction and photoluminescence experiments. The intersubband absorption spectrum of the Ga0.47In0.53As/InP, Ga0.38In0.62As0.80P0.20 (1.55 micrometers )/InP, and Ga0.27In0.73As0.57P0.43 (1.3 micrometers )/InP quantum wells are found to have cutoff wavelengths of 9.3 micrometers , 10.7 micrometers , and 14.2 micrometers respectively. These wavelengths are consistent with a conduction band offset to bandgap ratio of approximately 0.32. Facet coupled illumination responsivity and detectivity are reported for each composition.
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 have studied the dependence of the well doping density in n-type GaInAs/InP quantum well IR photodetectors (QWIPs) grown by low-pressure metalorganic chemical vapor deposition. Three identical GaInAs/InP QWIP structures were grown with well sheet carrier densities of 1 by 1011 cm-2, 3 by 1011 cm-2, and 10 by 1011 cm-2; all three samples had very sharp spectral response at (lambda) equals 9.0 micrometers . We find that there is a large sensitivity of responsivity, dark current, noise current, and detectivity with the well doping density. Measurements revealed that the lowest-doped samples had an extremely low responsivity relative to the doping concentration while the highest-doped sample had an excessively high dark current relative to doping. The middle-doped sample yielded the optimal results. This QWIP had a responsivity of 33.2 A/W and operated with a detectivity of 3.5 by 1010 cmHz1/2W-1 at a bias of 0.75 V and temperature of 80 K. This responsivity is the highest value reported for any QWIP in the (lambda) equals 8-9 micrometers range. Analysis is also presented explaining the dependence of the measured QWIP parameters to well doping density.
In order to tune the wavelength of lattice-matched QWIP detectors over the range from 4 - 20 microns, new designs are demonstrated for the first time which combine InGaAlAs and InGaAsP layers lattice-matched to InP and grown by gas-source molecular beam epitaxy. We demonstrate the first long- wavelength quantum well infrared photodetectors using the lattice-matched n-doped InGaAlAs/InP materials system. Samples with AlAs mole fractions of 0.0, 0.1, and 0.15 result in cutoff wavelengths of 8.5, 13.3, and 19.4 micrometer, respectively. A 45 degree facet coupled illumination responsivity of R equals 0.37 A/W and detectivity of D*(lambda ) equals 1 X 109 cm (root)Hz W-1 at T equals 77 K, for a cutoff wavelength (lambda) c equals 13.3 micrometer have been achieved. Based on the measured intersubband photoresponse wavelength, a null conduction band offset is expected for In0.52Ga0.21Al0.27As/InP heterojunctions. We also report quantum well infrared photodetector structures of In0.53Ga0.47As/Al0.48In0.52As grown on InP substrate with photoresponse at 4 micrometer suitable for mid-wavelength infrared detectors. These detectors exhibit a constant peak responsivity of 30 mA/W independent of temperature in the range from T equals 77 K to T equals 200 K. Combining these two materials, we report the first multispectral detectors that combine lattice-matched quantum wells of InGaAs/InAlAs and InGaAs/InP. Utilizing two contacts, a voltage tunable detector with (lambda) p equals 8 micrometer at a bias of V equals 5 V and (lambda) p equals 4 micrometer at V equals 10 V is demonstrated.
Dark current nose measurements were carried out between 10 and 104 Hz at T equals 80K on two InGaAs/InP quantum well IR photo detectors (QWIPs) designed for 8 micrometers IR detection. Using the measured noise data, we have calculated the thermal generation rate, bias-dependent gain, electron trapping probability, and electron diffusion length. The calculated thermal generation rate is similar to AlGaAs/GaAs QWIPs with similar peak wavelengths, but the gain is 50 X larger, indicating improved transport and carrier lifetime are obtained in the binary InP barriers. As a result, a large responsivity of 7.5 A/W at 5V bias and detectivity of 5 X 10$_11) cm (root) Hz/W at 1.2 V bias were measured for the InGaAs/InP QWIPs at T equals 80K.
We demonstrate long wavelength quantum well infrared photodetectors with GaAs quantum wells and GaInP barriers grown using gas-source molecular beam epitaxy. Wafers were grown with varying well widths. The optimum well width was 75 angstrom, which resulted in a detection peak at 13 micrometers and a cutoff wavelength of 15 micrometers . Dark current measurements of the samples with 15 micrometers cutoff wavelength show low dark current densities. The dark current characteristics have been investigated as a function of temperature and electron density in the well and compared to a model which takes into account thermionic emission and thermally assisted tunneling. The model is used to extract a saturation velocity of 1.5 X 105 cm/s for electrons. The photoelectron lifetime before recapture has been deduced from this carrier velocity and photoconductive gain measurements. The lifetime is found to be approximately 5 ps. Preliminary focal plane array imaging is demonstrated.
Acceptor doped, non-strained aluminum-free Quantum Well Intersubband Photodetectors lattice matched to GaAs with Ga0.79In0.21As0.59P0.41 wells and Ga0.62In0.38As0.22P0.78 barriers have been demonstrated on semi-insulating GaAs substrates. These devices which operate at normal incidence demonstrate a unique spectral response which extends from approximately 2 micrometers up to 10 micrometers . To explain such a broad spectral shape, a detailed theoretical analysis based on the 8 X 8 Kane Hamiltonian was necessary to probe all aspect of optical absorption. The results of this analysis revealed that spectral shape results from the influence of the Spin Split-off band on the band structure and the optical matrix.
High quality InSb has been grown by Molecular Beam Epitaxy and optimized using Reflection High Energy Electron Diffraction. A 4.8 micrometers InSb layer grown on GaAs at a growth temperature of 395 degree(s)C and a III/V incorporation ratio of 1:1.2 had an X-ray rocking curve FWHM of 158 arcsec and a Hall mobility of 92300 cm2V-1s-1 at 77 K, the best reported to date for InSb nucleated directly onto GaAs. InSb p-i-n structures of 5.8 micrometers grown under the same conditions demonstrated a X-ray Full Width at Half Maximum of 101 arcsec and 131 arcsec for GaAs and Si substrates, respectively, and exhibited excellent uniformity of +/- 3 arcsec over a 3' substrate. Prototype InSb p-i-n detectors on Si have been fabricated and have demonstrated photovoltaic response at 6.5 micrometers up to 200 K. These p-i-n detectors have also exhibited the highest D* for a device grown onto Si.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.