Photodiode Bias Research Articles

Thin-Film Photogate Pixel With Fixed Photodiode Bias for Near-Infrared Imaging

Thin-Film Photogate Pixel With Fixed Photodiode Bias for Near-Infrared Imaging

NBn-Photodiode Based on InAsSb/AlAsSb Alloys with a Long-Wavelength Cutoff of 5 μm

The results of studying the photoelectric characteristics of an nBn structure are presented. The photodiodes based on such structures may have a cutoff wavelength as high as 5 μm. Calculations based on these results show that such photodiodes have a threshold photosensitivity comparable with that of traditional analogs. An energy band diagram of the nBn structure is proposed based on experimental results and theoretical estimations; this diagram makes it possible to estimate the effect of potential barriers in the valence band of the wide-gap layer and at its boundaries with narrow-gap layers on the nBn-based photodiode sensitivity. The experimental results of studying the dependence of the photocurrent thermal-activation energy on the photodiode bias turned out to be important for developing the model.

Ultra-compact coherent receiver with serial interface for pluggable transceiver.

An ultra-compact integrated coherent receiver with a volume of 1.3 cc using a quad-channel transimpedance amplifier (TIA)-IC chip with a serial peripheral interface (SPI) is demonstrated for the first time. The TIA with the SPI and photodiode (PD) bias circuits, a miniature dual polarization optical hybrid, an octal-PD and small optical coupling system enabled the realization of the compact receiver. Measured transmission performance with 32 Gbaud dual-polarization quadrature phase shift keying signal is equivalent to that of the conventional multi-source agreement-based integrated coherent receiver with dual channel TIA-ICs. By comparing the bit-error rate (BER) performance with that under continuous SPI access, we also confirmed that there is no BER degradation caused by SPI interface access. Such an ultra-compact receiver is promising for realizing a new generation of pluggable transceivers.

A 0.5 V <formula formulatype="inline"><tex Notation="TeX">$< \hbox{4}\ \mu$</tex></formula>W CMOS Light-to-Digital Converter Based on a Nonuniform Quantizer for a Photoplethysmographic Heart-Rate Sensor

A 0.5 V CMOS light-to-digital converter (LDC) based on a nonuniform quantizer and off-chip photodiode enables a photodiode bias current (Ibias) range spanning 4 nA to 3.5 μA while consuming less than 4 μW of power. Using an off-chip LED as a modulated light source, measurements with a photodiode current signal having modulation frequency of 1.2 Hz (72 beats per minute) and 0.5% peak-to-peak amplitude relative to I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">bias</sub> performed at the low and high end of the Ibias range confirm over 30 dB of SNR for an integration bandwidth spanning 0.5 to 5 Hz. Using off-chip digital signal processing of the LDC output, instantaneous period jitter (a proxy for instantaneous heart rate) is measured to be less than 0.45% (rms) of the period, and the high sensitivity of the LDC allows detection of the heart-rate signal from a finger pressed against the off-chip photodiode using only ambient light. Key circuit components of the LDC include a wide range logarithmic digital-to-resistance converter (DRC) utilizing digital multibit ΔΣ modulation to achieve fine resolution and a nonuniform quantizer based on a laddered inverter quantizer (LIQAF) which also acts as a low-noise front-end amplifier and filter.

Wireless communication at 310 GHz using GaAs high-electron-mobility transistors for detection

We report on the first error-free terahertz (THz) wireless communication at 0.310 THz for data rates up to 8.2 Gbps using a 18-GHz-bandwidth GaAs/AlGaAs field-effect transistor as a detector. This result demonstrates that low-cost commercially-available plasma-wave transistors whose cut-off frequency is far below THz frequencies can be employed in THz communication. Wireless communication over 50 cm is presented at 1.4 Gbps using a uni-travelling-carrier photodiode as a source. Transistor integration is detailed, as it is essential to avoid any deleterious signals that would prevent successful communication. We observed an improvement of the bit error rate with increasing input THz power, followed by a degradation at high input power. Such a degradation appears at lower powers if the photodiode bias is smaller. Higher-data-rate communication is demonstrated using a frequency-multiplied source thanksto higher output power. Bit-error-rate measurements at data rates up to 10 Gbps are performed for different input THz powers. As expected, bit error rates degrade as data rate increases. However, degraded communication is observed at some specific data rates. This effect is probably due to deleterious cavity effects and/or impedance mismatches. Using such a system, realtime uncompressed high-definition video signal is successfully and robustly transmitted.

High-performance 320 × 256 long-wavelength infrared photodetector arrays based on CdHgTe layers grown by molecular beam epitaxy

This paper gives the parameters of 320 × 256 element long-wavelength infrared photodetectors fabricated by a new improved technology based on heteroepitaxial mercury-cadmium-tellur structures. In these photodetectors, the variation of the photodiode bias voltage over the area of the array is minimized; inefficient photodiode regions related to both hybridization and spike-shaped growth defects of epitaxial films are eliminated; the current-voltage characteristics of the diodes in the resulting photodetectors are homogeneous and are limited by the diffusion current component up to −400 mV. The dark current is 0.25–0.45 nA, and R 0 A = (0.6–3) · 102 Ω · cm2. The voltage sensitivity, the threshold irradiance, and the average NETD at the maximum sensitivity are 11.8 · 108 V/W, 3.7 · 10−8 W/cm2, and 26.8 mK, respectively. The percentage of defective elements is 1.5%.

Evidence of a Novel Source of Random Telegraph Signal in CMOS Image Sensors

This letter reports a new source of dark current random telegraph signal in CMOS image sensors due to meta-stable Shockley-Read-Hall generation mechanism at oxide interfaces. The role of oxide defects is discriminated thanks to the use of ionizing radiations. A dedicated RTS detection technique and several test conditions (radiation dose, temperature, integration time, photodiode bias) reveal the particularities of this novel source of RTS.

Silicon multiplexers for 1 × 576 HgCdTe IR focal-plane arrays

Two versions of silicon 1D multiplexer for 1 × 576 IR focal-plane arrays are designed, fabricated, and tested. The version LM-1 employs a direct-injection input circuit; the version LM-2 contains a buffered direct-injection circuit. They are intended for use with HgCdTe n +-p photodiodes operating in the wavelength ranges 8–14 and 3–5 μm, the minimum reverse diode resistance being 200 kΩ. The multiplexers ensure high uniformity of photodiode bias voltage; they are provided with a switched storage capacitance, which allows operation at different signal, background, and dark currents. Clocked at 3.5 MHz, they have an integration time of 40 μs and can read out 25 full-size (768 × 576) frames per second.

A 15-Gb/s 2.4-V Optical Receiver Using a Ge-on-SOI Photodiode and a CMOS IC

We report the fastest (15 Gb/s) and lowest voltage (2.4V) all-silicon-based optical receiver to date. The receiver consists of a lateral, interdigitated, germanium-on-silicon-on-insulator (Ge-on-SOI) photodiode wire-bonded to a 0.13-mum complementary metal-oxide-semiconductor (CMOS) receiver integrated circuit (IC). The photodiode has an external quantum efficiency of 52% at lambda=850 nm and a dark current of 10 nA at -2 V. The small-signal transimpedance of the receiver is 91-dBOmega and the bandwidth is 6.6 GHz. At a bit-error rate of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-12</sup> and lambda=850 nm; the receiver exhibits sensitivities of -11.0, -9.6, and -7.4 dBm at 12.5, 14, and 15 Gb/s, respectively. The receiver operates error-free at rates up to 10 Gb/s with an IC supply voltage as low as 1.5 V and with a photodiode bias as low as 0.5 V. The power consumption is 3 to 7 mW/Gb/s. The Ge-on-SOI photodiode is well suited for integration with CMOS processing, raising the possibility of producing high-performance, low-voltage, monolithically integrated receivers based on this technology in the future

10-Gb/s millimeter-wave signal generation using photodiode bias modulation

We present a simple 120-GHz-band millimeter-wave (MMW) modulation method that uses the bias-voltage dependence of unitraveling-carrier-photodiode output power, which we call photodiode (PD) bias modulation. We investigated the dependence of the output-power-saturation mechanisms on the bias voltage. We used a lowpass filter in the bias circuit to increase the modulation bandwidth, and the 3-dB modulation bandwidth was over 7 GHz. We demonstrated the modulation of 120-GHz MMW signals at a data rate of 10 Gb/s using PD bias modulation.

Nonlinearity in ESD Robust InGaAs p-i-n Photodiode

A guard ring (GR) protected InGaAs p-i-n photodiode with high linearity is fabricated and the effect of the GR protection structure on the linearity of the photodiode is studied. For the electrostatic discharge (ESD) protected photodiode, both the single second order (SSO) intermodulation and the single triple beat intermodulation are below 80 dBc. The GR can enhance the ESD robustness of the photodiode but degrades the photodiode's linearity about 3.5 dB for SSO at 854 MHz. The photodiode's nonlinearity is mainly due to the photodiode junction capacitance variation, which is caused by the photocurrent and bias voltage changes that are resulted from the change of incident laser power. The distortion caused by the photodiode's bias voltage is much larger than that caused by the photocurrent. The GR integrated into the photodiode aggregates the capacitance variation with the bias voltage and therefore increases the distortion. The calculated SSO distortion using the experimentally measured differential capacitances matches the experimental data.

Comprehension and modelling of heterojunction phototransistors operated in the Gummel-plot and common-emitter modes

Fabrication, characterization and modelling of heterojunction phototransistors (HPTs) are reported. The common-emitter (with current-biased base) and Gummel-plot (with voltage-biased base) modes are employed to characterize and fully comprehend what differences exist between the current- and voltage-biased HPT's performance. The results of further studies include the case when a series of different optical-power injection levels is illuminated at our HPTs. The performance of the current- and voltage-biased HPTs was also compared to that from a newly proposed HPT model and related equivalent circuit with good agreement found. Although an independent voltage source can be used to tune the operating point of a heterojunction bipolar transistor to a higher current level where the dc current gain is larger, the photocurrent generated within the base–collector (B–C) region offers few contributions to the final collector photocurrent. The optical gain obtained from the HPT biased using a high voltage is even smaller than that of the HPT with a floating base. It is concluded that (i) a current-biased HPT's dc base current and photocurrent generated within the B–C region entirely flow into the base–emitter (B–E) junction so that the device's optical gain is enhanced; (ii) however, no enhancement of optical gain for a HPT will be obtained using dc base bias, since the dc current gain is independent of collector (or base) current; (iii) a voltage-biased HPT behaves like a p–i–n photodiode and (iv) electrical base bias using a high external voltage source with a large series resistance is a possible way to enhance the optical gain of a HPT.

Investigation of GSO, LSO and YSO scintillators using reverse avalanche photodiodes

The performance characteristics of GSO, LSO and YSO scintillators coupled to new "reverse" avalanche photodiodes (ReAPD) were investigated and compared to those of BGO. The energy and timing resolutions were measured as a function of photodiode bias and amplifier shaping time constant. While the performance of BGO and GSO is critically dependent on these operating parameters because the signal-to-noise ratio is degraded by the dark and excess noise from the ReAPD, that of the high-luminosity LSO and YSO scintillators is not. The energy resolution in these crystals is demonstrated to be limited by the scintillator resolution. Further analysis indicates that excess variance in the number of photons generated in the crystal is mostly responsible for their disappointing energy resolution. This feature appears to be related to the important non-linearity in scintillation response as a function of incident gamma-ray energy observed for these high-luminosity scintillators.

Strained-layer InGaAs-GaAs-AlGaAs lasers with monolithically integrated photodiodes by selective-area MOCVD

Fabrication, design, and operation of strained layer, InGaAs-GaAs-AlGaAs lasers with monolithically integrated photodiodes fabricated by selective-area epitaxy are presented. Threshold currents as low as 8 mA (/spl sim/300 A/cm/sup 2/) were obtained for uncoated devices operating cw at room temperature. A responsivity of 71 /spl mu/A/mW was obtained for a device with a photodiode etched facet angle of 3/spl deg/ and a photodiode bias of 0 V. >

Constant False Alarm Rate Bias Control for an Avalanche Photodiode Laser Receiver

A constant false alarm rate closed loop controls avalanche photodiode bias over varying operating conditions such as temperature or ambient illumination and changes in photodiode parameters. The photodiode output is amplified, sensed in a threshold circuit, shaped to a constant amplitude and duration, and integrated. The integrator, also fed by a constant current representing the desired false alarm rate, generates an output proportional to the integrated error in false alarm rate. This control signal alters the photodiode bias until the integrated false alarm rate error is zero.