InP/InGaAsP avalanche photodiodes with new guard ring structure

A new guard ring structure for InP/InGaAsP avalanche photodiodes is described, which makes use of the impurity concentration difference between two InP epitaxial layers. The guard ring effect gives a low dark current and uniform multiplication characteristics at ? = 1.29 ?m.     

Elimination of the guard ring in uniform avalanche photodiodes

A conventionalp^{+}-n(orn^{+}-p) planar avalanche photodiode with a 10^-4cm²active area has ∼2.5 × 10^-4cm²total area because of its protecting guard ring and has a series resistance of ∼50 to 100 ohms. For narrow-band applications, multiplications greater than 10 are necessary to equal the available output power of a conventional nonavalanchingp-i-nphotodiode. In broad-band applications, significant multiplications are necessary to compete favorably with thep-i-nwhen the active area is less than 10^-4cm²or when the signal frequency is > 1 GHz. Ap-n^{+}planar structure is discussed that eliminates the need for a guard ring because positive junction curvature occurs on the high-resistivity side. Thep-n^{+}diodes can be designed to have resistances (Rs∼2 ohms), capacitances (C < 1 pf), and RC cutoff frequencies (fco>100 GHz) equivalent to those of thep-i-nand to have uniform multiplication as well. Closer array spacings can be achieved than with the guard ring structure, as well as higher effective quantum efficiencies in the avalanche mode. Practical realization of thep-n^{+}structure has been achieved in silicon by a combination of epitaxial and doped-oxide processing. Seven-mil-diameter junctions with high breakdown voltage (110 V) and uniform avalanche properties have been constructed.     

Planar InP/InGaAs avalanche photodiodes with preferential lateral extended guard ring

High-speed and high-sensitivity planar InP/InGaAs avalanche photodiodes (APD's) have been fabricated with a newly developed preferential lateral extended guard ring (PLEG). By employing the configuration, avalanche photodiode yield was markedly improved without edge breakdown. Received powers required to give 10^-9bit-error rate (BER) at 1.55-1.57-µm wavelength were -44.5 and -37.4 dBm for 450 Mbit/s and 2 Gbit/s, respectively.     

Excess noise in GaAs avalanche photodiodes with thin multiplicationregions

It is well known that the gain-bandwidth product of an avalanche photodiode can be increased by utilizing a thin multiplication region. Previously, measurements of the excess noise factor of InP-InGaAsP-InGaAs avalanche photodiodes with separate absorption and multiplication regions indicated that this approach could also be employed to reduce the multiplication noise. This paper presents a systematic study of the noise characteristics of GaAs homojunction avalanche photodiodes with different multiplication layer thicknesses. It is demonstrated that there is a definite “size effect” for multiplication regions less than approximately 0.5 μm. A good fit to the experimental data has been achieved using a discrete, nonlocalized model for the impact ionization process     

Planar InP avalanche photodiode with Zn-diffused guard ring

A guard ring structure with a p+-n?-n junction formed by Zn diffusion at 450°C gave a high gain planar InP avalanche photodiode. A maximum multiplication factor of more than 50 was obtained uniformly within the photosensitive area without edge breakdown.     

Low-temperature Zn- and Cd-diffusion profiles in InP and formation of guard ring in InP avalanche photodiodes

Zn and Cd diffusion in InP were studied in the wide temperature range of 350-580°C to realize a guard ring in InP avalanche photodiodes (APD's). Hole-concentration profiles for Zn and Cd diffusions at various temperatures were found to be expressed by a unified empirical curve, which decreases exponentially with the distance from the surface, and abruptly decreases at the diffusion front. A graded junction can be formed by diffusion at temperatures lower than 500°C for the n-InP background carrier concentration of 1016cm-3, while an abrupt junction can be formed by higher temperature diffusion. Breakdown voltages for the graded-junction diodes formed by low-temperature diffusion were confirmed to be higher than those for the abrupt-junction diodes formed by the higher temperature diffusion. A guard ring formed by the low-temperature Cd diffusion enabled planar-type InP and InGaAs/InP APD's to have uniform multiplication in the photosensitive area without any edge breakdown.     

Buried-mesa avalanche photodiodes

We have developed a low-cost buried-mesa avalanche photodiode (APD) primarily targeted for 2.5-Gb/s lightwave applications. These APDs are made by a simple batch process that produces a robust and reliable device with potentially high yield and thus low cost. The entire base structure of our InGaAs-InP APD is grown in one epitaxial step and the remaining process consists of four simple steps including a mesa etch, one epitaxial overgrowth, isolation, and metallization. Buried-mesa APDs fabricated in this way show high uniform gain that rises smoothly to breakdown with increasing reverse bias. When biased to operate at a gain of 10, these unoptimized devices show dark current less than 20 nA, excess noise factor less than 5, and a 3-dB bandwidth of about 4 GHz. With a 1550-nm laser modulated at 2488 Mb/s, a maximum sensitivity of -327 dBm was obtained with an optical receiver using one such APD, without antireflection coatings. These APD's not only demonstrate excellent device characteristics but also high reliability under rigorous stress testing. No degradation was observed even after being biased near breakdown for over 2000 h at 200°C     

Photon counting with silicon avalanche photodiodes

Avalanche photodiodes (APDs) are studied for use as photon-counting detectors. The APD may be biased slightly above (Geiger mode) or slightly below its voltage breakdown point. In the latter case, if the photon absorption rate is low enough, each individual photoelectron current pulse may be resolved with the use of a discriminator. APDs used in this photon-counting mode are shown to give the best performance at low light levels. Experimentally, overall photon detection probabilities of 5.0 and 0.33% were obtained at λ=820 nm and λ=1.064 μm, respectively, with a photon counter dead time as low as 15 ns and a dark current counting rate of 7000/s. The APD photon counter exhibited an exponential photon interarrival time probability density and a near-Poissonian photon-counting probability     

Parametric manufacturing yield modeling of GaAs/AlGaAs multiplequantum well avalanche photodiodes

GaAs/AlGaAs multiple quantum well (MQW) avalanche photodiodes (APD's) are of interest as an ultra-low noise image capture mechanism for high-definition systems. Since literally millions of these devices must be fabricated for imaging arrays, it is critical to evaluate potential performance variations of individual devices in light of the realities of semiconductor manufacturing. Specifically, even in a defect-free manufacturing environment, random variations in the fabrication process will lead to varying levels of device performance, Accurate device performance prediction requires precise characterization of these variations. This paper presents a systematic methodology for modeling the parametric performance of GaAs MQW APD's. The approach described requires a model of the probability distribution of each of the relevant process variables, as well as a second model to account for the correlation between this measured process data and device performance metrics. The availability of these models enables the computation of the joint probability density function required for predicting performance using the Jacobian transformation method. The resulting density function can then be numerically integrated to determine parametric yield. Since they have demonstrated the capability of highly accurate function approximation and mapping of complex, nonlinear data sets, neural networks are proposed as the preferred tool for generating the models described above. In applying this methodology to MQW APD's, it is shown that using a small number of test devices with varying active diameters, barrier and well widths, and doping concentrations enables prediction of the expected performance variation of APD gain and noise in larger populations of devices. This approach compares favorably with Monte Carlo techniques and allows device yield prediction prior to high volume manufacturing in order to evaluate the impact of both design decisions and process capability     

Improved germanium avalanche photodiodes

New kinds of germanium avalanche photodiodes with n+-n-p and p+-n structures were devised for improved excess noise and high quantum efficiency performance. Multiplication noise, quantum efficiency, and pulse response were studied and compared with those of the conventional n+-p structure diode. Multiplication noise of the new type of diodes were measured in the wavelength range between 0.63 and 1.52 μm. The effective ionization coefficient ratio of the p+-n diode was lower than unity at a wavelength longer than 1.1 μm and 0.6-0.7 at 1.52 μm, and that of the n+-n-p diode was 0.6-0.7 in the whole sensitive wavelength region. Response times were evaluated by using a mode-locked Nd:YAG laser beam and a frequency bandwidth wider than 1 GHz was estimated. Receiving optical power levels were compared with each other using parameters measured in this study.     

HgCdTe electron avalanche photodiodes

Exponential-gain values well in excess of 1,000 have been obtained in HgCdTe high-density, vertically integrated photodiode (HDVIP) avalanche photodiodes (APDs) with essentially zero excess noise. This phenomenon has been observed at temperatures in the range of 77–260 K for a variety of cutoff wavelengths in the mid-wavelength infrared (MWIR) band, with evidence of similar behavior in other IR bands. A theory for electron avalanche multiplication has been developed using density of states and electron-interaction matrix elements associated with the unique band structure of HgCdTe, with allowances being made for the relevant scattering mechanisms of both electrons and holes at these temperatures. This theory is used to develop an empirical model to fit the experimental data obtained at DRS Infrared Technologies. The functional dependence of gain on applied bias voltage is obtained by the use of one adjustable parameter relating electron energy to applied voltage. A more quantitative physical theory requires the use of Monte Carlo techniques incorporating the preceding scattering rates and ionization probabilities. This has been performed at the University of Texas at Austin, and preliminary data indicate good agreement with DRS models for both avalanche gain and excess noise as a function of applied bias. These data are discussed with a view to applications at a variety of wavelengths.     

Multi-element reachthrough avalanche photodiodes

Two approaches to making multi-element arrays of p⁺-π-p-n⁺reachthrough avalanche photodiodes are reported. In the first approach a single common avalanche region (p-layer) for all elements is used, with the segmentation between elements being on the p⁺layer. This approach has the advantage of having zero dead space between adjacent elements, but is difficult to fabricate, and has a very narrow range of operation in which it is neither noisy due to injection nor suffers from poor element-to-element isolation. In a second approach, the p⁺contact is common and separate avalanche regions are used. The problem for this case is the width of the dead space between adjacent elements which, because of field-fringing effects, is considerably wider than the actual physical distance between elements. A self-aligning technique is described for fabricating arrays by the second approach and the technique demonstrated with a 25-element linear array on 300-µm centers. The measured dead space is in the 60-80 µm range, depending on the gain. The array can be used at an average gain of 100 or more, has excellent element-to-element isolation, and NEP's below 2 × 10¹⁵W/Hz^1/2at 800-900 nm and below 10^-14W/ Hz^1/2over the whole spectral range from 400 to 1060 nm.     

Planar-structure InP/InGaAsP/InGaAs avalanche photodiodes withpreferential lateral extended guard ring for 1.0-1.6 μm wavelengthoptical communication use

A planar InP-based InGaAs heterostructure avalanche photodiode (APD) with a preferential lateral extended guard ring is proposed. Optimum design and device fabrication are described for the planar-structure APD using various-donor-concentration n-InP avalanche layers, separated from the light-absorbing InGaAs layer. High performance results are low dark current, high speed, low noise, and uniform avalanche gain without edge breakdown. The APD yielded a sensitivity as high as -37.4 dBm for a 2-Gb/s 1.57-μm wavelength return-to-zero sequence with 10^-9 bit error rate     

InP-lnGaAsP planar avalanche photodiodes with self-guard-ring effect

Marked diode characteristics dependence on the distance between p-n junction and heterointerface in double heterojunction InP-InGaAsP planar a.p.d.s is described. In a diode with an optimised configuration, as high as 3000 maximum avalanche gain and less than 3×10?6 A/cm2 dark-current density at 0.9 VB are achieved.     

Dead-space-based theory correctly predicts excess noise factor forthin GaAs and AlGaAs avalanche photodiodes

The conventional McIntyre carrier multiplication theory for avalanche photodiodes (APDs) does not adequately describe the experimental results obtained from APDs with thin multiplication-regions. Using published data for thin GaAs and Al_0.2Ga_0.8As APDs, collected from multiplication-regions of different widths, we show that incorporating dead-space in the model resolves the discrepancy. The ionization coefficients of enabled carriers that have traveled the dead space are determined as functions of the electric field, within the confines of a single exponential model for each device, independent of multiplication-region width. The model parameters are determined directly from experimental data. The use of these physically based ionization coefficients in the dead-space multiplication theory, developed earlier by Hayat et al. provide excess noise factor versus mean gain curves that accord very closely with those measured for each device, regardless of multiplication-region width. It is verified that the ratio of the dead-space to the multiplication-region width increases, for a fixed mean gain, as the width is reduced. This behavior, too, is in accord with the reduction of the excess noise factor predicted by the dead-space multiplication theory     

Pulse response of avalanche photodiodes

A study has been made of the time response of heterostructure avalanche photodiodes for InGaAs and InP/InGaAs material systems. A transfer/scattering matrix method, where the matrix parameters are related to the ionization coefficients, has been used. A time domain study has been carried out to find the time variation of electron and hole number densities and currents     

Silicon Geiger mode avalanche photodiodes

In this letter we present the results regarding the electrical and optical characterization of Geiger mode silicon avalanche photodiodes(GMAP) fabricated by silicon standard planar technology. Low dark count rates,negligible afterpulsing effects,good timing resolution and high quantum detection efficiency in all the visible range have been measured. The very good electro-optical performances of our photodiodes make them attractive for the fabrication of arrays with a large number of GMAP to be used both in the commercial and the scientific fields,as telecommunications and nuclear medical imaging.     

外保护环短路不能减小光电二极管暗电流

通过理论和实验证明了外保护环短路的光电二极管不仅不能减小暗电流,相反会增加暗电流。因此想用外保护环短路,以求减小光电二极管暗电流的方法是不可行的。其结果与预期的正好相反。     

High-speed metal-semiconductor-metal photodiodes with Er-doped GaAs

Very high-speed MSM photodiodes have been fabricated on Er-doped GaAs over a doping range of 10¹⁸-10²⁰ cm^-3 . The impulse response (characterized by photoconductive sampling) of these diodes, with finger widths/spacings of 2 μm, has been found to be tunable over a range of about 3 ps-22 ps. Electro-optic sampling was used to characterize MSM diodes with finger widths/spacings of 0.5 μm and 1 μm on a sample with [Er]=10¹⁹ cm^-3, resulting in 3-dB bandwidths of 160 GHz and 140 GHz, respectively, corresponding to pulse widths of 2.7 ps and 3.3 ps. Correlation measurements were also done on the GaAs:Er samples, using an all-electronic Sampling Optical Temporal Analyzer (SOTA) structure     

Arrays of Geiger mode avalanche photodiodes

Following our previous work which has led us to fabricate single pixels of geiger mode avalanche photodiodes (GMAPs), we present in this letter the results regarding the fabrication and characterization of a bidimensional array of GMAPs. Low dark count rates and very good uniformity over the sensor are reported. High quantum efficiency in the visible range has been measured. Measurements indicate that not all the nominal active area is effectively sensitive. We have some preliminary evidence that no crosstalk effects are present in our device. Notwithstanding this, in view of a near future shrinking of all dead regions, an optical trench process has been developed and is illustrated here. Possible future trends are highlighted.