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ABSTRACT: The history-dependent recurrence theory for mul-tiplication noise in avalanche photodiodes (APDs), developed by Hayat et al., is generalized to include inter-layer boundary effects in heterostructure APDs with multilayer multiplication regions. These boundary effects include the initial energy of injected carriers as well as bandgap-transition effects within a multilayer multiplication region. It is shown that the excess noise factor can be significantly reduced if the avalanche process is initiated with an energetic carrier, in which case the initial energy serves to reduce the initial dead space associated with the injected carrier. An excess noise factor reduction up to 40% below the traditional thin-APD limit is predicted for GaAs, depending on the operational gain and the multiplication-region's width. The gen-eralized model also thoroughly characterizes the behavior of dead space as a function of position across layers. This simultaneously captures the effect of the nonuniform electric field as well as the anticipatory nature of inter-layer bandgap-boundary effects. Such anticipatory behavior of the dead space is ignored in simplified models where the dead space is assumed to change abruptly at the layer boundary. The theory is applied to recently fabricated thin Al 0 6 Ga 0 4 As/GaAs heterostructure APDs exhibiting low excess noise factors. The excess noise factor predictions are in very good agreement with experiment. In one device, where the initial-energy effect is pronounced, the measured excess noise factor is 36% below the value predicted by previous analytical multiplication models which ignore the initial-energy effect.
IEEE Transactions on Electron Devices 01/2114; 49. · 2.32 Impact Factor
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ABSTRACT: Four-element modified uni-traveling-carrier (MUTC) photodiode arrays (PDA) flip-chip bonded onto transmission lines on AlN substrates are demonstrated. High RF output powers of 26.2 dBm and 21.0 dBm are achieved at 35 GHz and 48 GHz, respectively, using a PDA with 28-μm diameter photodiodes. A systematic comparison between a PDA with four 20 μm-diameter elements and a discrete detector with the same active area (40-μm diameter) is presented. The PDA achieved higher output power and thermal dissipation compared to its discrete counterpart.
Optics Express 04/2013; 21(8):9967-73. · 3.59 Impact Factor
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ABSTRACT: The performance of 34-μm-diameter InGaAs/InP charge compensated modified uni-traveling carrier photodiodes (CC MUTCs) is studied
using a commercial device simulator based on a drift-diffusion model. Excellent agreement has been achieved between simulations
and experiments. The origin of the degradation of responsivity at high optical injection level is investigated. Parameters
of the photodiode are further optimized to maximize the saturation current without sacrificing bandwidth and responsivity.
Optical and Quantum Electronics 04/2012; 40(1):41-46. · 0.82 Impact Factor
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ABSTRACT: We demonstrate a flip-chip bonded modified uni-traveling carrier (MUTC) photodiode with an RF output power of 0.75 W (28.8 dBm) at 15 GHz and OIP3 as high as 59 dBm. The photodiode has a responsivity of 0.7 A/W, 3-dB bandwidth > 15 GHz, and saturation photocurrent > 180 mA at 11 V reverse bias.
Optics Express 12/2011; 19(26):B385-90. · 3.59 Impact Factor
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ABSTRACT: Natural lithography with 100-nm-diameter SiO(2) spheres followed by inductively coupled plasma etching was used to texture the surface of 4H-SiC for a wide-spectrum large-acceptance-angle anti-reflective layer. The surface showed low normal-incidence reflectance of < 5% over a wide spectrum from 250 nm to 550 nm. Photodiodes fabricated from the surface-textured SiC showed broader spectral and angular responsivity than SiC photodiodes with SiO(2) antireflective coating. The textured SiC photodiodes showed peak responsivity of 116 mA/W, large angle of acceptance angle (< 2% decrease in responsivity at 50° incident angle) and low dark current at 10V.
Optics Express 11/2011; 19(24):23664-70. · 3.59 Impact Factor
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ABSTRACT: Near ultraviolet-sensitive separate absorption and multiplication avalanche photodiodes with GaN/SiC epitaxial layers grown on SiC substrate were fabricated. Dark current < 1 pA at 90% breakdown voltage, maximum multiplication gain of ∼105, and responsivity exceeding 4.2 A/W at 365 nm were achieved.
Applied Physics Letters 09/2011; 99(13):131110-131110-3. · 3.84 Impact Factor
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ABSTRACT: Gallium Phosphide (GaP) reach-through avalanche photodiodes (APDs) are reported. The APDs exhibited dark current less than a pico-ampere at unity gain. A quantum efficiency of 70% was achieved with a recessed window structure; this is almost two times higher than previous work.
Optics Express 09/2011; 19(20):19607-12. · 3.59 Impact Factor
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ABSTRACT: A femtosecond-laser-textured Si photodetector is reported. Broadband spectral optical response is detected from UV to NIR. A quantum efficiency of greater than 80% from 490 nm to 780 nm has been achieved. The quantum efficiency at 245 nm is 62%, which is comparable to UV-enhanced Si photodiodes. The bandwidth of a 250-μm-diameter device is 60 MHz.
Applied Optics 06/2011; 50(17):2508-11. · 1.41 Impact Factor
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ABSTRACT: An improved gated-mode passive quenching with active reset (gated-PQAR) circuit is utilized in conjunction with an InGaAs/InP single-photon avalanche photodiode (SPAD). Photon detection efficiency (PDE) and dark count probability (DCP) were measured at a gate repetition rate of 1 MHz. The reduced afterpulsing afforded by the gated-PQAR circuit enabled measurement of afterpulsing for hold-off times as short as 10 ns. The timing resolution (jitter) for different excess biases has also been investigated. At 230 K and an excess bias of 2.5 V, 0.3% afterpulse probability for a 10 ns hold-off time was achieved with 13% PDE, 2 × 10−6 DCP, 160 ps jitter, and 0.2 ns effective gate width. For the same hold-off time, at a higher excess bias of 3.5 V, 30% PDE, 1 × 10−5 DCP and 120 ps jitter were achieved with 7% afterpulse probability with an effective gate width of 0.7 ns.
Journal of Modern Optics 02/2011; 58(Nos. 3–4):201-209. · 1.17 Impact Factor
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ABSTRACT: A transient response technique that is widely used to measure the minority carrier lifetime in inorganic semiconductors is proposed to measure the lifetime of free polarons in a polymer:fullerene bulk heterojunction (BHJ) solar cell. A numerical model that can be used to describe the transient behavior of BHJ devices has been developed. Using the proposed method, the lifetime of free polarons in poly (3-hexylthiophene) and [6, 6]-phenyl C61-butyric acid methyl ester blend film is estimated to be in the range of 300–400 ns.
Journal of Applied Physics. 10/2010; 108(8):084511-084511-5.
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ABSTRACT: There are a number of mature and emerging applications that require the ultimate in sensitivity, i.e., single photon detection. A promising candidate is the single photon avalanche diode (SPAD). Its performance is measured in terms single photon detection efficiency, dark count probability (dark count rate), operating temperature, spectral response, jitter, and afterpulsing. Quenching circuits for SPADs have also become active areas of research. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
physica status solidi (c) 06/2010; 7(10):2536 - 2539.
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ABSTRACT: A simple technique to incorporate microlenes with small photodiode arrays is demonstrated and analyzed. Using this method, the fill factor was increased from 2.6% to 22.4% for a two by two array. Simulation results are also shown. The photocurrent with microlens was approximately 8.6 times larger than without the microlens, which is consistent with simulation results.
Optics Express 05/2010; 18(11):11713-9. · 3.59 Impact Factor
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ABSTRACT: The third-order intermodulation distortions of InGaAs/InP modified uni-traveling carrier photodiodes with a highly-doped p-type absorber are characterized. The third-order local intercept point is 55 dBm at low frequency (< 3 GHz) and remains as high as 47.5 dBm up to 20 GHz. The frequency characteristics of the OIP3 are well explained by an equivalent circuit model.
Optics Express 10/2009; 17(22):20221-6. · 3.59 Impact Factor
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ABSTRACT: In this work we report a separate-absorption-charge-multiplication Ge/Si avalanche photodiode with an enhanced gain-bandwidth-product of 845 GHz at a wavelength of 1310 nm. The corresponding gain value is 65 and the electrical bandwidth is 13 GHz at an optical input power of -30 dBm. The unconventional high gain-bandwidth-product is investigated using device physical simulation and optical pulse response measurement. The analysis of the electric field distribution, electron and hole concentration and drift velocities in the device shows that the enhanced gain-bandwidth-product at high bias voltages is due to a decrease of the transit time and avalanche build-up time limitation at high fields.
Optics Express 08/2009; 17(15):12641-9. · 3.59 Impact Factor
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ABSTRACT: The effectiveness of thin SiGe buffer layers in terminating threading dislocations and reducing photodiode dark current for Ge epitaxially grown on Si (001) has been investigated. The structural morphology of the films was studied by atomic force microscopy and transmission electron microscopy. The dark current of Ge on Si photodiodes can be reduced by over an order of magnitude by incorporating two different composition SiGe buffer layers. The origin of dark current and the effectiveness of thermal annealing the SiGe layers were also studied
IEEE Journal of Quantum Electronics 04/2007; · 1.88 Impact Factor
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ABSTRACT: An In<sub>0.53</sub>Ga<sub>0.47</sub>As-InP avalanche photodiode with very low dark current (0.15 pA at 95% breakdown voltage, 200 K) has been characterized in gated mode for single-photon detection. The temperature dependence of dark current and dark count yields activation energy of ~0.4 eV from 240 K to 297 K. High single-photon detection efficiency (SPDE) at telecom wavelengths with very low dark count rate (DCR) (e.g., DCR =12 kHz at SPDE =45% at 1.31 mum and 200 K) was achieved
IEEE Photonics Technology Letters 04/2007; · 2.19 Impact Factor
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ABSTRACT: Backside-illuminated germanium photodiodes fabricated on silicon substrate with two Si <sub>x</sub>Ge<sub>1-x</sub> buffer layers are reported. At 1.3 mum, the responsivity was 0.62 A/W for reverse bias greater than 0.1 V. The 3-dB bandwidth was 21.5 GHz at 10-V reverse bias, achieving a bandwidth-efficiency product of 12.6 GHz
IEEE Journal of Selected Topics in Quantum Electronics 12/2006; · 3.78 Impact Factor
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ABSTRACT: Photodetectors fabricated on microstructured silicon are reported. The photodetectors exhibited high photoresponse; at 3 V bias, the responsivities were 92 A/W at 850 nm and 119 A/W at 960 nm. At wavelengths longer than 1.1 μm, the photodetectors still showed strong photoresponse. A generation-recombination gain mechanism has been proposed to explain the photoresponse of these photodiodes. From measurements of the noise current density, the calculated gain was approximately 1200 at 3 V bias.
Applied Physics Letters 07/2006; 89(3):033506-033506-3. · 3.84 Impact Factor
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ABSTRACT: We identify a new shot noise suppression mechanism in a thin (approximately 100 nm) heterostructure avalanche photodiode. In the low-gain regime the shot noise is suppressed due to temporal correlations within amplified current pulses. We demonstrate in a Monte Carlo simulation that the effective excess noise factors can be < 1, and reconcile the apparent conflict between theory and experiments. This shot noise suppression mechanism is independent of known mechanisms such as Coulomb interaction, or reflection at heterojunction interfaces.
Physical Review Letters 10/2005; 95(17):176604. · 7.37 Impact Factor
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ABSTRACT: We report photodiodes fabricated on Ge grown on Si substrate. The Ge growth was preceded by two SixGe1−x buffer layers. Dark current as low as 1.07 μA was achieved at 10 V reverse bias for 24 μm-diam mesa devices. At 1.3 μm wavelength, the responsivity was 0.37 A∕W at 0 V and 0.57 A∕W when above 2 V reverse bias. The 3 dB bandwidth was 8.1 GHz at a reverse bias of 10 V.
Applied Physics Letters 10/2004; 85(15):3286-3288. · 3.84 Impact Factor
