A low dark current InGaAs/InP p-i-n photodiode with covered mesa structure

A new InGaAs p-i-n photodiode with a covered mesa (CM) structure having extremely low dark current characteristics and high yields has been developed. The device consists of only two epitaxial layers: n^--InP and n^--InGaAs, continuously grown on an n⁺-InP substrate by liquid-phase epitaxy. The InGaAs layer is chemically etched to be a tapered shape in order to make the fabrication process simple, as compared with a conventional mesa diode. The Zn diffusion to form a p-n junction is carried out without a diffusion mask such as Si3N4or SiO2, which induces damage due to the thermal stress. The tapered-shape InGaAs layer is covered with the Zn-diffused layer because a surface p-n junction occurring in an InGaAs region is leaky. Therefore, the surface p-n junction of the photodiode appears in the n^--InP layer, which has a bandgap about two times wider than the InGaAs. Finally, the passivation of the surface p-n junction is carried out with a Si3N4film formed by a plasma-assisted chemical vapor deposition. We have successfully achieved an extremely low dark current of 20 pA at a reverse bias voltage of 10 V and a high yield of 80 percent, by adopting the CM structure and the simple fabrication process.     

Twelve-channel individually addressable InGaAs/InP p-i-n photodiode and InGaAsP/InP LED arrays in a compact package

We report on monolithically integrated 1 × 12 arrays of In0.53Ga0.47As p-i-n detectors and InGaAsP LED's for use in long-wavelength optical communication system applications. The detectors are sensitive in the wavelength region of0.95-1.65 mum, and the LED's emit at 1.30 μm. The devices utilize Si V-block fiber array connectors with one end polished at a 45° angle with respect to the fiber axis such that the optical path is bent by 90° to afford coupling laterally to the photonic device. The resultant structures are built in a 14-pin dual-in-line (DIP) compact metal package, and are capable of operation at least up to 200 Mbit/s.     

A numerical analysis of a heterostructure InP/InGaAs photodiode

Electrical properties of a heterostructure InP/In0.53Ga0.47- As photodiode have been analyzed numerically. A device simulator, which can handle a heterostructure up to a high voltage operation, was developed for this work. The numerical simulator explains the experimental results obtained regarding photocurrent. The band-gap discontinuities, i.e., 0.22 eV for the conduction band and 0.37 eV for the valence band, were confirmed to be plausible. The photocurrent switching mechanism in the photodiode by bias voltage was clarified through carrier and potential distributions. It was revealed that the photo-excited holes accumulate at the heterointerface, and the switching voltage for photocurrent varies according to the incident optical power level. It is expected that this simulator will be a powerful tool for optimum heterostructure photodiode design.     

Analysis of InGaAs p-i-n photodiode frequency response

The frequency response of a InGaAs p-i-n diode was analyzed to better characterize the high-speed performances required for high-bit-rate optical communication systems. The carrier concentration and the photocurrent density in the intrinsic region were obtained analytically. The derived equations led to the frequency response which takes into account both the influence of the electric field on the carrier velocities and their nonuniform generation. In addition, the impulse response was computed by inverse Fourier transform techniques. Comparing the results with those obtained by assuming the carrier velocities independently of the electric field, discrepancies were found in the electrical power bandwidth up to 25%, and in the FWHM up to 45%     

Easily manufactured high-speed back-illuminated GaInAs/InP p-i-n photodiode

A back-illuminated planar GaInAs/InP p-i-n photodiode has been fabricated with a simple fabrication process to obtain a high-speed detector. The photodiode has a capacitance as low as 54 fF, a dark current of about 3 pA, and a quantum efficiency of 74% at a 1.55- mu m wavelength. A cutoff frequency of 31 GHz was obtained when the photocurrent was about 500 mu A and the bias voltage was -10 V.<>     

Cryogenic performance of a high-speed GaInAs/InP p-i-n photodiode

The cryogenic performance of a high-speed GaInAs/InP p-i-n photodiode, with graded bandgap layers at the heterostructure interfaces, was investigated for the first time. DC measurements show that the dark current of the diode decreases sharply as the temperature decreases from 300 to 200 K. A factor of 1000 in dark current reduction was found for this photodiode, when it was cooled from room temperature to about 150 K. Similar modulation bandwidths were found for this device for temperatures between 9 and 300 K, with a bandwidth greater than 20 GHz. No degradation was found in performance at cryogenic temperature compared to room temperature. This enables direct integration of high-speed photodiodes with superconductive and other cryogenic electronics     

An InP/InGaAs p-i-n/HBT monolithic transimpedance photoreceiver

A monolithically integrated 1-Gb/s p-i-n/HBT transimpedance photoreceiver is discussed. The optoelectronic integrated circuit (OEIC) was made from metalorganic vapor-phase epitaxy (MOVPE)-grown InP/InGaAs heterostructures and had a transimpedance of 1375 Ω, a sensitivity of -26.1 dBm, >25-dB dynamic range, and a 500-MHz bandwidth     

Two-dimensional simulation of large-area InGaAs/InP p-i-n photodiodes

A stationary physical model of the p-i-n photodiode based on a two-dimensional drift-diffusion scheme of charge transport in multilayer In_xGa_1-x As_yP_1-y /InP heterostructures is developed. The model takes into account the Fermi statistics for electrons and holes, charge carrier mobility dependence on the electric field and impurity concentration, as well as thermionic emission and tunneling at the heterointerfaces. The effect of design parameters on the characteristics of large area p-i-n photodiodes is analyzed and methods for increasing their dynamic range are suggested.     

Multiplication-dependent frequency responses of InP/InGaAs avalanche photodiode

The intrinsic response time of InP/InGaAs APD has been reported. The multiplication factor dependent frequency responses were measured up to multiplication factor of 24. The results show the gain bandwidth of InP/InGaAs APDs is 10 GHz, and the intrinsic response time to be 16 ps.     

Locally ion-implanted JFET in an InGaAs/InP p-i-n photodiode layerstructure for a monolithically planar integrated receiver OEIC

A novel planar concept for the monolithic integration of a p-i-n photodiode (PD) and a junction field-effect transistor (JFET) is described. In an otherwise optimized InGaAs/InP PD layer sequence, grown by metalorganic vapor-phase epitaxy (MOVPE), a local Si- and Be-ion implantation has been performed to realize a thin n⁺-doped channel layer and a buried p-layer for the JFET. JFETs (1.6×290 μm) have a maximum transconductance of 100 mS/mm and a cutoff frequency of 7 GHz. PDs with 64-μm diameter show a dark current of 1 nA at -10 V, a responsivity of 1.1 A/W, and a 3-dB bandwidth of 7.6 GHz. The PD-JFET combination exhibits a clear open eye pattern at 200 Mb/s. A receiver sensitivity of -35 dBm for a bit error rate of 10^-9 is estimated     

Cadmium sulfide passivation of InGaAs/InP mesa p-i-n photodiodes

A cadmium sulfide (CdS) passivation process was demonstrated for the first time on InGaAs/InP p-i-n mesa photodetectors. The passivated devices produced lower reverse bias leakage currents in comparison to devices that received only a thermally deposited SiO₂ film. The subsequent deposition of SiO₂ on the passivated devices produced virtually no change to the aforementioned leakage currents even after undergoing a 3-h, 300°C thermal treatment. In contrast, similar SiO₂ capped devices, fabricated without the CdS passivating layer, show a large increase in leakage current when subjected to the same thermal cycle. Leakage current versus mesa diameter measurements suggest these results are due to reduce surface recombination at the exposed mesa sidewall. X-ray photoelectron spectroscopy (XPS) results indicate the S:Cd ratio of these films to be 0.77.     

Planar embedded InP/GaInAs p-i-n photodiode for very high-speed operation

Planar embedded InP/GaInAs p-i-n photodiodes have been fabricated by using preferential ion-beam etching for planarizing and embedding the p-i-n photodiode structure in a semi-insulating InP substrate. The stray capacitances caused by a bonding pad and an interconnection have been markedly reduced, which resulted in extremely low capacitance of less than 0.08 pF for a diameter of 20 μm of photosensitive area. It has been demonstrated by an optical heterodyne technique that the photodiode exhibits a maximum cutoff frequency of 14 GHz. This result was analyzed taking the depletion layer thickness into account and has been found to be dominated by the carrier transit time. The demonstrated low capacitance and high-speed response result indicates the suitability of the p-i-n photodiodes not only for a discrete p-i-n photodiode but also for optoelectronic integration.     

Ultrafast, dual-depletion region, InGaAs/InP p-i-n detector

The design of a new kind of photodetector, the dual-depletion region p-i-n photodetector, is presented. This vertical detector has a parasitic capacitance and transit time that can be controlled semi-independently. This eases the classical tradeoff between these two speed limiting factors, allowing the design of large, fast detectors. A theoretical analysis of the transit time effect and the capacitance effect is made. This analysis is then used to compute optimum design parameters     

Flip-chip planar GaInAs/InP p-i-n photodiode array for paralleloptical transmission

A back-illuminated planar GaInAs/InP p-i-n photodiode array with a simple fabrication process was developed for application to parallel optical transmission. Four p-i-n photodiodes were integrated in the array. The average capacitance and dark current were as low as 0.12 pF and 8 pA, respectively, at -5 V. At a 1.55-μm wavelength, the quantum efficiency of each photodiode was over 80%. The cutoff frequency was 8-10 GHz with four photodiodes when the bias voltage was -3 V and the load resistance was 50 Ω. Crosstalk between channels was -12 dB at the cutoff frequency and -45 dB at 1 GHz     

InGaAs avalanche photodiode with InP p-n junction

A new InGaAs avalanche photodiode structure that has an InGaAs light absorption region and InP avalanche multiplying region is proposed. A dark-current density of 2.2 × 10?3 A/cm2 at 90% of breakdown voltage and a multiplication factor of 45 were obtained for the new structure diode fabricated from a liquid-phase epitaxially grown wafer.     

High speed InGaAs/InP p-i-n photodiodes fabricated on asemi-insulating substrate

High speed, mass-produced InGaAs-InP p-i-n photodiodes have been fabricated on a semi-insulating substrate. The FWHM (full width at half maximum) impulse response of a 25-μm² device has been measured to be under 16 ps, entirely limited by the measurement system. The high speed of this structure was achieved by scaling the area down to 25 μm² and the intrinsic layer thickness down to 0.3 μm. Further scaling of this structure is possible, and bandwidths in excess of 200 GHz should be achievable. This structure is also useful for integration with bias tees, matching networks, and optical and electronic preamplifiers     

High quantum efficiency, long wavelength InP/InGaAs microcavity photodiode

There is a inherent tradeoff between the quantum efficiency and bandwidth of conventional PIN photodiodes. In the case of devices based on III-V semiconductors, an absorption region thickness of approximately 2 mu m is required to achieve quantum efficiencies greater than 80%, although this limits the transit-time-limited bandwidth to less than 15 GHz. It has recently been shown that a microcavity photodiode can circumvent this performance tradeoff and achieve both high quantum efficiency and large bandwidths. The fabrication of a microcavity PIN photodiode with a high quantum efficiency near 1.55 mu m is described. An external quantum efficiency of 82% at 1480 nm has been achieved with an InGaAs absorption layer only 2000 AA thick embedded in a resonant cavity grown by metal organic vapor phase epitaxy (MOVPE).<>     

High-speed-response InGaAs/InP heterostructure avalanche photodiode with InGaAsP buffer layers

The optical response time of an InGaAs/InP heterostructure avalanche photodiode (HAPD) with InGaAsP buffer layers is reported. It is shown that the buffer layers play an important role in reduction of the pile-up effect and are considered to be effective in achieving high-speed InGaAs/InP HAPDs.     

New type InGaAs/InP heterostructure avalanche photodiode with buffer layer

A new type heterostructure avalanche photodiode (HAPD) is proposed and successfully fabricated by liquid phase epitaxy and Zn-diffusion. The HAPD has been made from a successively grown wafer which consists of In0.53Ga0.47As light absorption layer, InGaAsP buffer layers and InP avalanche multiplication layer on n-InP substrate. Dark current density of 1 × 10^-4Acm^-2at 0.9 VBis achieved. When illuminating with 1.15 µm light, the diode has a maximum multiplication gain of 880 and an external quantum efficiency of 40%. The quantum efficiency is markedly improved than that of previously reported HAPD.     

Reliability of InGaAs/InP long-wavelength p-i-n photodiodes passivated with polyimide thin film

The long-term reliability of InGaAs/InP p-i-n photodiodes passivated with polyimide thin film was studied through a room temperature life test and through thermally accelerated life tests. No degradation in dark current was observed in a room temperature life test at a reverse bias of -15 V after aging for 7000 h. However, the dark current increased gradually in the accelerated life tests at 110°C, 130°C, and 150°C. It was confirmed that the activation energy of degradation in dark current was 0.85 eV and the average lifetime was estimated to be 10⁷h at room temperature. The dark current recovered in high temperature storage tests. The phenomenon of degradation and recovery was qualitatively explained by a model of accumulation and diffusion of mobile ions at a junction perimeter.