Center for Quantum Devices - Most Downloaded Journal Articles

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15.	A hybrid green light-emitting diode comprised of n-ZnO/(InGaN/GaN) multi-quantum-wells/p-GaN C. Bayram, F. Hosseini Teherani, D.J. Rogers and M. Razeghi Applied Physics Letters, Vol. 93, No. 8, p. 081111-1-- August 25, 2008 ...[Visit Journal] Hybrid green light-emitting diodes (LEDs) comprised of n-ZnO/(InGaN/GaN) multi-quantum-wells/p-GaN were grown on semi-insulating AlN/sapphire using pulsed laser deposition for the n-ZnO and metal organic chemical vapor deposition for the other layers. X-ray diffraction revealed that high crystallographic quality was preserved after the n-ZnO growth. LEDs showed a turn-on voltage of 2.5 V and a room temperature electroluminescence (EL) centered at 510 nm. A blueshift and narrowing of the EL peak with increasing current was attributed to bandgap renormalization. The results indicate that hybrid LED structures could hold the prospect for the development of green LEDs with superior performance. [reprint (PDF)]
15.	High power broad area quantum cascade lasers Y. Bai, S. Slivken, S.R. Darvish, A. Haddadi, B. Gokden and M. Razeghi Applied Physics Letters, Vol. 95, No. 22, p. 221104-1-- November 30, 2009 ...[Visit Journal] Broad area quantum cascade lasers (QCLs) are studied with ridge widths up to 400 µm, in room temperature pulsed mode operation at an emission wavelength around 4.45 µm. The peak output power scales linearly with the ridge width. A maximum total peak output power of 120 W is obtained from a single 400-µm-wide device with a cavity length of 3 mm. A stable far field emission characteristic is observed with dual lobes at ±38° for all tested devices, which suggests that these broad area QCLs are highly resistant to filamentation. [reprint (PDF)]
15.	High-power λ ~ 9.5 µm quantum-cascade lasers operating above room temperature in continuous-wave mode J.S. Yu, S. Slivken, A. Evans, S.R. Darvish, J. Nguyen, and M. Razeghi Applied Physics Letters, 88 (9)-- February 27, 2006 ...[Visit Journal] We report high-power continuous-wave (cw) operation of λ~9.5 μm quantum-cascade lasers to a temperature of 318 K. A high-reflectivity-coated 19-μm-wide and 3-mm-long device exhibits cw output powers as high as 150 mW at 288 K and still 22 mW at 318 K. In cw operation at 298 K, a threshold current density of 1.57 kA/cm², a slope efficiency of 391 mW/A, and a maximum wall-plug efficiency of 0.71% are obtained. [reprint (PDF)]
15.	High power, high wall-plug efficiency, high reliability, continuous-wave operation quantum cascade lasers at Center for Quantum Devices Razeghi, Manijeh SPIE Proceedings Volume 11296, Optical, Opto-Atomic, and Entanglement-Enhanced Precision Metrology II; 112961C-- February 25, 2020 ...[Visit Journal] Since the demonstration of the first quantum cascade laser (QCL) in 1997, QCLs have undergone considerable developments in output power, wall plug efficiency (WPE), beam quality, wavelength coverage and tunability. Among them, many world-class breakthroughs were achieved at the Center for Quantum Device at Northwestern University. In this paper, we will discuss the recent progress of our research and present the main contributions of the Center for Quantum Devices to the QCL family on high power, high wall-plug efficiency (WPE), continuous-wave (CW) and room temperature operation lasers. [reprint (PDF)]
15.	Advanced Monolithic Quantum Well Infrared Photodetector Focal Plane Array Integrated with Silicon Readout Integrated Circuit J. Jiang, S. Tsao, K. Mi, M. Razeghi, G.J. Brown, C. Jelen and M.Z. Tidrow Infrared Physics and Technology, 46 (3)-- January 1, 2005 ...[Visit Journal] Today, most infrared focal plane arrays (FPAs) utilize a hybrid scheme. To achieve higher device reliability and lower cost, monolithic FPAs with Si based readout integrated circuits (ROICs) are the trend of the future development. In this paper, two approaches for monolithic FPAs are proposed: double sided integration and selective epitaxy integration. For comparison, the fabrication process for hybrid quantum well infrared photodetectors (QWIP) FPAs are also described. Many problems, such as the growth of QWIPs on Si substrate and processing incompatibility between Si and III–V semiconductors, need to be solved before monolithic FPAs can be realized. Experimental work on GaInAs/InP QWIP-on-Si is given in this paper. A record high detectivity of 2.3×10⁹ jones was obtained for one QWIP-on-Si detector at 77 K. [reprint (PDF)]
15.	High-Power Continuous-Wave Operation of a 6 µm Quantum-Cascade Laser at Room Temperature J.S. Yu, S. Slivken, A. Evans, L. Doris, and M. Razeghi Applied Physics Letters, 83 (13)-- September 29, 2003 ...[Visit Journal] We report continuous-wave (cw) operation of quantum-cascade lasers (λ= 6 µm) using a thick electroplated Au top contact layer and epilayer-up bonding on a copper heat sink up to a temperature of 308 K (35 °C). The high cw optical output powers of 132 mW at 293 K and 21 mW at 308 K are achieved with threshold current densities of 2.29 and 2.91 kA/cm², respectively, for a high-reflectivity-coated 15 µm wide and 2 mm long laser. [reprint (PDF)]
15.	Development of Quantum Well Infrared Photodetectors at the Center for Quantum Devices M. Razeghi, M. Erdtmann, C. Jelen, J. Diaz, F. Guastavino, G.J. Brown, and Y.S. Park Infrared Physics and Technology 42 (3-5)-- January 1, 2001 ...[Visit Journal] Results of detector characterization are presented for quantum well infrared photodetectors (QWIPs) fabricated from a variety of III-V material systems lattice-matched to GaAs or InP substrate, p-Type GaAs/GaInP QWIPs show background limited performance up to temperatures of 120 K, while p-type GaInAsP/GaInAsP QWIPs exhibit broadband response from lambda = 2.5-10 mum. n-Type GaAs/GaInP QWIPs are sensitive deep into the VLWIR with very low dark current. Extremely large responsivities of 33.2 AW(-1) were obtained from n-type GaInAs/InP QWIPs operating at lambda = 9 mum. Devices made from n-type AlGaInAs/InP and GaInAs/AlInAs have also been realized that extend the wavelength range of sensitivity from 3 mum out to 20 mum while remaining lattice-matched to InP. Lattice-matched multispectral detectors are demonstrated for sensitivity at both 4 and 8.5 mum 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 read-out integrated circuitry. [reprint (PDF)]
14.	Type II superlattice infrared detectors and focal plane arrays Vaidya Nathan; Manijeh Razeghi Proc. SPIE 6542, Infrared Technology and Applications XXXIII, 654209 (May 14, 2007)-- May 14, 2007 ...[Visit Journal] Type II superlattce photodetectors have recently experienced significant improvements in both theoretical structure design and experimental realization. Empirical Tight Binding Method is initiated and developed for Type II superlattice. Growth characteristics such as group V segregation and incorporation phenomena are taken into account in the model and shown higher precision. A new Type II structure, called M-structure, is introduced and theoretically demonstrated high R₀A, high quantum efficiency. Device design is optimized to improve the performance. As a result, 55% quantum efficiency and 10 Ohm·cm² R₀A are achieved for an 11.7 μm cut-off photodetector at 77K. FPA imaging at longwavelength is demonstrated with a capability of imaging up to 171K. At 81K, the noise equivalent temperature difference presented a peak at 0.33K. [reprint (PDF)]
14.	Pulsed metalorganic chemical vapor deposition of high quality AlN/GaN superlattices for intersubband transitions C. Bayram, B. Fain, N. Pere-Laperne, R. McClintock and M. Razeghi SPIE Proceedings, San Jose, CA Volume 7222-12-- January 26, 2009 ...[Visit Journal] A pulsed metalorganic chemical vapor deposition (MOCVD) technique, specifically designed for high quality AlN/GaN superlattices (SLs) is introduced. Optical quality and precise controllability over layer thicknesses are investigated. Indium is shown to improve interface and surface quality. An AlN/GaN SL designed for intersubband transition at a telecommunication wavelength of ~1.5 µm, is grown, and processed for intersubband (ISB) absorption measurements. Room temperature measurements show intersubband absorption centered at 1.49 µm. Minimal (n-type) silicon doping of the well is shown to be crucial for good ISB absorption characteristics. The potential to extend this technology into the far infrared and even the terahertz (THz) region is also discussed. [reprint (PDF)]
14.	Comparison of the Physical Properties of GaN Thin Films Deposited on (0112) and (0001) Sapphire Substrates C.J. Sun and M. Razeghi Applied Physics Letters 63 (7)-- August 16, 1993 ...[Visit Journal] A direct comparison of the physical properties of GaN thin films is made as a function of the choice of substrate orientations. Gallium nitride single crystals were grown on (0001) and (0112) sapphire substrates by metalorganic chemical vapor deposition. Better crystallinity with fine ridgelike facets is obtained on the (0112) sapphire. Also lower carrier concentration and higher mobilities indicate both lower nitrogen vacancies and less oxygen incorporation on the (0112) sapphire. The results of this study show better physical properties of GaN thin films achieved on (0112) sapphire. [reprint (PDF)]
14.	First observation of the two‐dimensional properties of the electron gas in Ga0.49In0.51P/GaAs heterojunctions grown by low pressure metalorganic chemical vapor deposition M. Razeghi; P. Maurel; F. Omnés; S. Ben Armor; L. Dmowski; J. C. Portal M. Razeghi, P. Maurel, F. Omnés, S. Ben Armor, L. Dmowski, J. C. Portal; First observation of the two‐dimensional properties of the electron gas in Ga0.49In0.51P/GaAs heterojunctions grown by low pressure metalorganic chemical vapor deposition. Appl. Phys. Lett. 12 May 1986; 48 (19): 1267–1269-- June 12, 1986 ...[Visit Journal] We report the first observation of a two‐dimensional electron gas from Shubnikov–de Haas and quantum hall effect experiments in GaInP/GaAs heterostructures grown by low pressure metalorganic chemical vapor deposition. Angular‐dependent Shubnikov–de Haas measurements confirm two dimensionality of the system. Low‐temperature persistent photoconductivity was observed. Critical density at which the second electric subband starts to be populated was determined to be 7.3×1011 cm−2. [reprint (PDF)]
14.	Continuous wave quantum cascade lasers with 5.6 W output power at room temperature and 41% wall-plug efficiency in cryogenic operation F. Wang, S. Slivken, D. H. Wu, Q. Y. Lu, and M. Razeghi AIP Advances 10, 055120-- May 19, 2020 ...[Visit Journal] In this paper, we report a post-polishing technique to achieve nearly complete surface planarization for the buried ridge regrowth processing of quantum cascade lasers. The planarized device geometry improves the thermal conduction and reliability and, most importantly, enhances the power and efficiency in continuous wave operation. With this technique, we demonstrate a high continuous wave wall-plug efficiency of an InP-based quantum cascade laser reaching ∼41% with an output power of ∼12 W from a single facet operating at liquid nitrogen temperature. At room temperature, the continuous wave output power exceeds the previous record, reaching ∼5.6 W. [reprint (PDF)]
14.	Recent progress of quantum cascade laser research from 3 to 12 μm at the Center for Quantum Devices MANIJEH RAZEGHI,* WENJIA ZHOU,STEVEN SLIVKEN,QUAN-YONG LU,DONGHAI WU, AND RYAN MCCLINTOC Applied Optics Vol. 56, No. 31 -- October 10, 2017 ...[Visit Journal] The quantum cascade laser (QCL) is becoming the leading laser source in the mid-infrared (mid-IR) range, which contains two atmospheric transmission windows and many molecular fingerprint absorption features. Since its first demonstration in 1994, the QCL has undergone tremendous development in terms of the output power, wall plug efficiency, wavelength coverage, tunability and beam quality. At the Center for Quantum Devices, we have demonstrated high-power continuous wave operation of QCLs covering a wide wavelength range from 3 to 12 μm, with power output up to 5.1 W at room temperature. Recent research has resulted in power scaling in pulsed mode with up to 203 W output, electrically tunable QCLs based on monolithic sampled grating design, heterogeneous QCLs with a broad spectral gain, broadly tunable on-chip beam-combined QCLs, QCL-based mid-IR frequency combs, and fundamental mode surface emitting quantum cascade ring lasers. The developed QCLs will be the basis for a number of next-generation spectroscopy and sensing systems. [reprint (PDF)]
14.	Development of Quantum Cascade Lasers for High Peak Output Power and Low Threshold Current Density S. Slivken and M. Razeghi Solid State Electronics 46-- January 1, 2002 ...[Visit Journal] Design and material optimization are used to both decrease the threshold current density and increase the output power for quantum cascade lasers. Waveguides are designed to try and minimize free-carrier and surface-plasmon absorption. Excellent material characterization is also presented, showing excellent control over layer thickness, interface quality, and doping level. Experiments are done to both optimize the injector doping level and to maximize the output power from a single aperture. At 300 K, a threshold current density as low as 1.8 kA/cm² is reported, along with peak powers of approximately 2.5 W. Strain-balanced lasers are also demonstrated at λnot, vert, similar5 μm, exhibiting threshold current densities<300 A/cm² at 80 K. These values represent the state-of-the-art for mid-infrared lasers with λ>4 μm [reprint (PDF)]
14.	Crack-free AlGaN for solar-blind focal plane arrays through reduced area expitaxy E. Cicek, R. McClintock, Z. Vashaei, Y. Zhang, S. Gautier, C.Y. Cho and M. Razeghi Applied Physics Letters, Vol. 102, No. 05, p. 051102-1-- February 4, 2013 ...[Visit Journal] We report on crack reduction for solar-blind ultraviolet detectors via the use of a reduced area epitaxy (RAE) method to regrow on patterned AlN templates. With the RAE method, a pre-deposited AlN template is patterned into isolated mesas in order to reduce the formation of cracks in the subsequently grown high Al-content Al_xGa_1−xN structure. By restricting the lateral dimensions of the epitaxial growth area, the biaxial strain is relaxed by the edges of the patterned squares, which resulted in ∼97% of the pixels being crack-free. After successful implementation of RAE method, we studied the optical characteristics, the external quantum efficiency, and responsivity of average pixel-sized detectors of the patterned sample increased from 38% and 86.2 mA/W to 57% and 129.4 mA/W, respectively, as the reverse bias is increased from 0 V to 5 V. Finally, we discussed the possibility of extending this approach for focal plane array, where crack-free large area material is necessary for high quality imaging. [reprint (PDF)]
14.	High-quality visible-blind AlGaN p-i-n photodiodes E. Monroy, M. Hamilton, D. Walker, P. Kung, F.J. Sanchez, and M. Razeghi Applied Physics Letters 74 (8)-- February 22, 1999 ...[Visit Journal] We report the fabrication and characterization of Al_xGa_1−xN p-i-n photodiodes (0 < x < 0.15) grown on sapphire by low-pressure metalorganic chemical vapor deposition. The devices present a visible rejection of six orders of magnitude with a cutoff wavelength that shifts from 365 to 338 nm. 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. This behavior is justified by the strong frequency dependence of the device capacitance. By an admittance analysis, we conclude that speed is not limited by deep levels, but by substitutional Mg capture and emission time. [reprint (PDF)]
14.	Back-illuminated separate absorption and multiplication GaN avalanche photodiodes J.L. Pau, C. Bayram, R. McClintock, M. Razeghi and D. Silversmith Applied Physics Letters, Vol. 92, No. 10, p. 101120-1-- March 10, 2008 ...[Visit Journal] The performance of back-illuminated avalanche photodiodes with separate absorption and multiplication regions is presented. Devices with an active area of 225 µm² show a maximum multiplication gain of 41,200. The calculation of the noise equivalent power yields a minimum value of 3.3×10⁻¹⁴ W·Hz^−1/2 at a gain of 3000, increasing to 2.0×10⁻¹³ W·Hz^−1/2 at a gain of 41,200. The broadening of the response edge has been analyzed as a function of bias. [reprint (PDF)]
14.	Positive and negative luminescence in binary Type-II InAs/GaSb superlattice photodiodes D. Hoffman and M. Razeghi SPIE Conference, San Jose, CA, Vol. 6127, pp. 61271H-- January 23, 2006 ...[Visit Journal] In the present work, we show measurements of both positive and negative luminescence of binary Type-II InAs/GaSb superlattice photodiodes in the 3 to 13 μm spectral range. Through a radiometric calibration technique, we demonstrate temperature independent negative luminescence efficiencies of 45 % in the midwavelength (MWIR) sample from 220 K to 320 K without anti-reflective coating and values reaching 35 % in the long wavelength infrared (LWIR) spectrum sample. [reprint (PDF)]
14.	InP-based quantum-dot infrared photodetectors with high quantum efficiency and high temperature imaging S. Tsao, H. Lim, H. Seo, W. Zhang and M. Razeghi IEEE Sensors Journal, Vol. 8, No. 6, p. 936-941-- June 1, 2008 ...[Visit Journal] We report a room temperature operating InAs quantum-dot infrared photodetector grown on InP substrate. The self-assembled InAs quantum dots and the device structure were grown by low-pressure metalorganic chemical vapor depositon. The detectivity was 6 x 10¹⁰cm·Hz^1/2·W^-1 at 150 K and a bias of 5 V with a peak detection wavelength around 4.0 micron and a quantum efficiency of 48%. Due to the low dark current and high responsivity, a clear photoresponse has been observed at room temperature. A 320 x 256 middle wavelength infrared focal plane array operating at temperatures up to 200 K was also demonstrated. The focal plane array had 34 mA/W responsivity, 1.1% conversion efficiency, and noise equivalent temperature difference of 344 mK at 120 K operating temperature. [reprint (PDF)]
14.	High-Power Continuous-Wave Operation of Quantum-Cascade Lasers Up to 60 °C J.S. Yu, A. Evans, J. David, L. Doris, S. Slivken and M. Razeghi IEEE Photonics Technology Letters, 16 (3)-- March 1, 2004 ...[Visit Journal] High-temperature high-power continuous-wave (CW) operation of high-reflectivity-coated 12 μm wide quantum-cascade lasers emitting at λ = 6 μm with a thick electroplated Au top contact layer is reported for different cavity lengths. For a 3 mm long laser, the CW optical output powers of 381 mW at 293 K and 22 mW at maximum operating temperature of 333 K (60°C) are achieved with threshold current densities of 1.93 and 3.09 kA/cm², respectively. At 298 K, the same cavity gives a maximum wall plug efficiency of 3.17% at 1.07 A. An even higher CW optical output power of 424 mW at 293 K is obtained for a 4-mm-long laser and the device also operates up to 332 K with an output power of 14 mW. Thermal resistance is also analyzed at threshold as a function of cavity length. [reprint (PDF)]
14.	Crystallography of epitaxial growth of wurtzite-type thin films on sapphire substrates P. Kung, C.J. Sun, A. Saxler, H. Ohsato, and M. Razeghi Journal of Applied Physics 75 (9)-- May 1, 1994 ...[Visit Journal] In this article, we present a crystallographic model to describe the epitaxial growth of wurtzite‐type thin films such as gallium nitride (GaN) on different orientations of sapphire (Al2O3) substrates. Through this model, we demonstrate the thin films grown on (00⋅1)Al₂O₃ have a better epilayer‐substrate interface quality than those grown on (01⋅2)Al₂O₃. We also show the epilayer grown on (00⋅1)Al₂O₃ are gallium‐terminated, and both (00⋅1) and (01⋅2) surfaces of sapphire crystals are oxygen‐terminated. [reprint (PDF)]
14.	Highly Conductive Co-Doped Ga2O3Si-In Grown by MOCVD Junhee Lee, Honghyuk Kim, Lakshay Gautam and Manijeh Razeghi Coatings 2021, 11(3), 287; https://doi.org/10.3390/coatings11030287 ...[Visit Journal] We report a highly conductive gallium oxide doped with both silicon and indium grown on c-plane sapphire substrate by MOCVD. From a superlattice structure of indium oxide and gallium oxide doped with silicon, we obtained a highly conductive material with an electron hall mobility up to 150 cm2/V·s with the carrier concentration near 2 × 1017 cm−3. However, if not doped with silicon, both Ga2O3:In and Ga2O3 are highly resistive. Optical and structural characterization techniques such as X-ray, transmission electron microscope, and photoluminescence, reveal no significant incorporation of indium into the superlattice materials, which suggests the indium plays a role of a surfactant passivating electron trapping defect levels. [reprint (PDF)]
14.	Aluminum nitride films on different orientations of sapphire and silicon K. Dovidenko, S. Oktyabrsky, J. Narayan, and M. Razeghi Journal of Applied Physics79 (5)-- March 1, 1996 ...[Visit Journal] The details of epitaxial growth and microstrictural characteristics of AlN films grown on sapphire (0001), (1012) and Si (100), (111) substrates were investigated using plan‐view and cross‐sectional high‐resolution transmission electron microscopy and x‐ray diffraction techniques. The films were grown by metalorganic chemical vapor deposition using TMA1+NH3+N2 gas mixtures. Different degrees of epitaxy were observed for the films grown on α‐Al₂O₃ and Si substrates in different orientations. The epitaxial relationship for (0001) sapphire was found to be (0001)AlN∥(0001)sap with in‐plane orientation relationship of [0110]AlN∥[1210]sap. This is equivalent to a 30° rotation in the basal (0001) plane. For (1012) sapphire substrates, the epitaxial relationship was determined to be (1120)AlN∥(1012)sap with the in‐plane alignment of [0001]AlN∥[1011]sap. The AlN films on (0001) α‐Al₂O₃ were found to contain inverted domain boundaries and a/3〈1120〉 threading dislocations with the estimated density of 10¹⁰ cm⁻². The density of planar defects (stacking faults) found in AlN films was considerably higher in the case of (1012) compared to (0001) substrates. Films on Si substrates were found to be highly textured c axis oriented when grown on (111) Si, and c axis textured with random in‐plane orientation on (100) Si. The role of thin‐film defects and interfaces on device fabrication is discussed. [reprint (PDF)]
14.	Long-term reliability of Al-free InGaAsP/GaAs λ = 808 nm) lasers at high-power high-temperature operation J. Diaz, H. Yi, M. Razeghi and G.T. Burnham Applied Physics Letters 71 (21)-- November 24, 1997 ...[Visit Journal] We report the long-term reliability measurement on uncoated Al-free InGaAsP/GaAs (λ = 808 nm) lasers at high-power and high-temperature operation. No degradation in laser performance has been observed for over 30 ,000 h of lifetime testing in any of randomly selected several 100 μm-wide uncoated lasers operated at 60 °C with 1 W continuous wave output power. This is the first and the most conclusive evidence ever reported that directly shows the high long-term reliability of uncoated Al-free lasers. [reprint (PDF)]
14.	Comparison of PLD-Grown p-NiO/n-Ga2O3 Heterojunctions on Bulk Single Crystal β-Ga2O3 and r-plane Sapphire Substrates D. J. Rogers , V. E. Sandana, F. Hosseini Teherani and M. Razeghi Proc. of SPIE Vol. 12895, Quantum Sensing and Nano Electronics and Photonics XX, 128870J (28 January - 1 February 2024 San Francisco)doi: 10.1117/12.3012511 ...[Visit Journal] p-NiO/n-Ga2O3 heterostructures were formed on single crystal (-201) β (monoclinic) Ga2O3 and r-sapphire substrates by Pulsed Laser Deposition. Ring mesa layer stacks were created using a shadow mask during growth. X-Ray diffraction studies were consistent with the formation of (111) oriented fcc NiO on the bulk Ga2O3 and randomly oriented fcc NiO on (102) oriented β-Ga2O3 /r-sapphire. RT optical transmission studies revealed bandgap energy values of ~3.65 eV and ~5.28 eV for the NiO and Ga2O3 on r-sapphire. p-n junction devices were formed by depositing gold contacts on the layer stacks using shadow masks in a thermal evaporator. Both heterojunctions showed rectifying I/V characteristics. On bulk Ga2O, the junction showed a current density over 16mA/cm2 at +20V forward bias and a reverse bias leakage current over 3 orders of magnitude lower at -20V (1 pA). On Ga2O3/r-sapphire the forward bias current density at +15V was about an order of magnitude lower than for the p-NiO/bulk n-Ga2O3 heterojunction while the reverse bias leakage current at -15V (~ 20 pA) was an order of magnitude higher. Hence the NiO/bulk Ga2O3 junction was more rectifying. Upon illumination with a Xenon lamp a distinct increase in current was observed for the IV curves in both devices (four orders of magnitude for -15V reverse bias in the case of the p-NiO/bulk n-Ga2O3 heterojunction). The p-NiO/n-Ga2O3/rsapphire junction gave a spectral responsivity with a FWHM value of 80nm and two distinct response peaks (with maxima at 230 and 270nm) which were attributed to carriers being photogenerated in the Ga2O3 underlayer. For both devices time response studies showed a 10%/90% rise and fall of the photo generated current upon shutter open and closing which was relatively abrupt (millisecond range), and there was no evidence of significant persistent photoconductivity. [reprint (PDF)]

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