Edge breakdown in 4H-SiC avalanche photodiodes

We report suppression of edge breakdown in mesa-structure SiC avalanche photodiodes (APDs) by employing a 10/spl deg/ sidewall bevel. These devices exhibit low dark currents, <10 pA for a 160-/spl mu/m-diameter device, at the onset of avalanche gain. Two-dimensional raster scans of both beveled and nonbeveled devices, fabricated from the same wafer, show the photocurrent as a function of position and illustrate the spatial properties of avalanche gain in SiC APDs.     

4H-SiC avalanche photodiode with multistep junction extensiontermination

4H-SiC avalanche photodiodes (APDs) are fabricated with a multistep junction termination extension. The leakage current density has been dramatically reduced to as low as 1 μA/cm² and photo-responsivity up to 10⁵ A/W has been achieved. The 4H-SiC APDs can run very stably at power densities up to 10⁴ W/cm²     

Study of reverse dark current in 4H-SiC avalanche photodiodes

Temperature-dependent current-voltage (I-V) measurements have been used to determine the reverse dark current mechanisms in 4H-SiC avalanche photodiodes (APDs). A pn junction vertical mesa structure, passivated with SiO/sub 2/ grown by plasma enhanced chemical vapor deposition, exhibits predominate leakage current along the mesa sidewall. Similar APDs, passivated by thermal oxide, exhibit lower dark current before breakdown; however, when the temperature is higher than 146/spl deg/C, an anomalous dark current, which increases rapidly with temperature, is observed. This current component appears to be eliminated by the removal of the thermal oxide. Near breakdown, tunneling is the dominant dark current mechanism for these pn devices. APDs fabricated from a pp/sup -/n structure show reduced tunneling current. At room temperature, the dark current at 95% of breakdown voltage is 140 fA (1.8 nA/cm/sup 2/) for a 100-/spl mu/m diameter APD. At a gain of 1000, the dark current is 35 pA (0.44 /spl mu/A/cm/sup 2/).     

Trapping phenomena in avalanche photodiodes on nanosecond scale

A technique for measuring the release of minority carriers emitted from deep levels in avalanche photodiodes (APDs) at operating conditions is discussed. The method, time-correlated carrier counting (TCCC), is very sensitive and accurate. Densities of filled traps were measured down to 10⁹ cm^-3 and lifetimes in the nanosecond range. This technique can be useful in tailoring gettering processes for APDs and in studies of traps at high electric fields     

Gain-bandwidth characteristics of thin avalanche photodiodes

The frequency-response characteristics of avalanche photodiodes (APDs) with thin multiplication layers are investigated by means of a recurrence technique that incorporates the history dependence of ionization coefficients. In addition, to characterize the autocorrelation function of the impulse response, new recurrence equations are derived and solved using a parallel computer. The mean frequency response and the gain-bandwidth product are computed and a simple model for the dependence of the gain-bandwidth product on the multiplication-layer width is set forth for GaAs, InP, Al_0.2Ga_0.8As, and In_0.52Al_0.48 As APDs. It is shown that the dead-space effect leads to a reduction (up to 30%) in the bandwidth from that predicted by the conventional multiplication theory. Notably, calculation of the power-spectral density of the photocurrent reveals that the presence of dead space also results in a reduction in the fluctuations in the frequency response. This result is the spectral generalization of the reduction in the excess noise factor in thin APDs and reveals an added advantage of using thin APDs in ultrafast receivers     

Impact-ionization and noise characteristics of thin III-V avalanchephotodiodes

It is, by now, well known that McIntyre's localized carrier-multiplication theory cannot explain the suppression of excess noise factor observed in avalanche photodiodes (APDs) that make use of thin multiplication regions. We demonstrate that a carrier multiplication model that incorporates the effects of dead space, as developed earlier by Hayat et al. provides excellent agreement with the impact-ionization and noise characteristics of thin InP, In_0.52 Al_0.48As, GaAs, and Al_0.2Ga_0.8As APDs, with multiplication regions of different widths. We outline a general technique that facilitates the calculation of ionization coefficients for carriers that have traveled a distance exceeding the dead space (enabled carriers), directly from experimental excess-noise-factor data. These coefficients depend on the electric field in exponential fashion and are independent of multiplication width, as expected on physical grounds. The procedure for obtaining the ionization coefficients is used in conjunction with the dead-space-multiplication theory (DSMT) to predict excess noise factor versus mean-gain curves that are in excellent accord with experimental data for thin III-V APDs, for all multiplication-region widths     

GaN avalanche photodiodes operating in linear-gain mode and Geigermode

For solar-blind ultraviolet detection, AlGaN avalanche photodiodes (APDs) that operate in Geiger mode can outperform conventional AlGaN photodiodes in sensitivity and should compare favorably to photomultiplier tubes. Toward this goal, we report GaN APDs that operate in the linear-gain mode and in the Geiger mode. The APDs were fabricated from high-quality GaN epitaxial layers grown by hydride vapor phase epitaxy. The GaN layer structure consisted of a Zn-doped π layer, an unintentionally doped n layer, and a Si-doped n+ layer-all on top of a thick GaN unintentionally doped n layer on a sapphire substrate. Capacitance-voltage (C-V) measurements on photodiodes fabricated from some of these layers show that field strengths between 3 and 4 MV/cm are sustainable in the depletion region at voltages slightly below the observed breakdown of ~80 V. Both mesa-etched and planar devices exhibited avalanche gains of 10 in linear-gain mode and ~10⁶ in Geiger mode when top illuminated with a 325 nm HeCd laser. Raster measurements of the photoresponse show highly uniform response in gain mode that becomes slightly more inhomogeneous in Geiger mode     

Design and Characteristics of Guardring-Free Planar AlInAs Avalanche Photodiodes

This paper reports a guardring-free planar AlInAs avalanche photodiode (APD) for optical fiber communications. AlInAs APDs can achieve a larger gain-bandwidth product (GBP) with lower excess noise than commercial InP APDs, and the guardring-free planar structure enables these superior AlInAs APDs to have both a low dark current and high reliability for practical use. We present the structure, fabrication, designs, APD characteristics, and receiver sensitivity, systematically. The guardring-free planar structure and its peculiarities are described, and we show APD designs for 2.5-Gb/s and 10-Gb/s applications and their characteristics. A 0.2-mum -thick AlInAs multiplication layer achieves a GBP of 120 GHz and an excess noise factor of 2.9 at a multiplication factor of 10. Their dark currents are less than 20 nA and their lifetime is evaluated to be 25 million hours at 85^degC. Lastly, we demonstrate that the guardring-free planar AlInAs APDs with a transimpedance amplifier achieve the remarkable sensitivity of -37.0 dBm at a bit error rate of 10^-10 for 2.5-Gb/s signals and of -29.9 dBm at a bit error rate of 10^-12 for 10-Gb/s signals. This performance indicates that the guardring-free planar AlInAs APDs have made great advances against commercial InP APDs and other AlInAs APDs.     

Performance of Deep Ultraviolet GaN Avalanche Photodiodes Grown by MOCVD

We report high-performance GaN ultraviolet (UV) p-i-n avalanche photodiodes (APDs) fabricated on bulk GaN substrates. The fabricated GaN p-i-n diodes demonstrated optical gains > 10⁴ and low dark current densities operating at wavelengths from 280 to 360 nm. The result is among the highest III-N-based APD gains at the deep UV wavelength of 280 nm reported to date.     

Guardring-Free Planar AlInAs Avalanche Photodiodes for 2.5-Gb/s Receivers With High Sensitivity

We demonstrate a practical 2.5-Gb/s AlInAs avalanche photodiode (APD) and an AlInAs APD-based optical receiver with high sensitivity. The AlInAs APD has a simple guardring-free planar structure with high reliability. In addition to the inherent low excess noise of AlInAs, their simplicity and high yields are great advantages in production, even when contrasted with the planar InP APDs now on the market. The guardring-free AlInAs APDs achieve larger gain-bandwidth (GB) products and lower excess noise, with a maximum 3-dB bandwidth of 6.0 GHz and a GB product of typically 80 GHz, and have equal performance with InP APDs, which have a responsivity of 1.0 A/W and a multiplying dark current of 2.2 nA. An AlInAs APD-based 2.5-Gb/s optical receiver with a SiGe transimpedance amplifier has a sensitivity of -37.0 dBm at a bit-error rate of 10^-10     

Temperature dependence of the ionization coefficients of AlxGa1-xAs

As Al_xGa_1-xAs alloys are increasingly used for microwave and millimeter wave power devices and circuits that work under high electric field intensities and junction temperatures; understanding the temperature dependence of impact ionization and related properties in this material system becomes more and more important. Measurements of the multiplication gain and noise of avalanche photodiodes (APDs) provide insight to the avalanche characteristics of semiconductors. Previously, we have reported the characteristics of GaAs and Al_0.2Ga_0.8As APD's at room temperature. In this paper, the gain and noise of a series of homojunction Al_xGa_1-xAs APD's were investigated over a wide temperature range from 29°C to 125°C, and the temperature dependence of their ionization coefficients was extracted     

Geiger-Mode Operation of GaN Avalanche Photodiodes Grown on GaN Substrates

Ultraviolet (UV) GaN p-i-n avalanche photodiodes (APDs) on low dislocation density free-standing GaN substrates were grown and fabricated. The GaN APD showed a stable avalanche multiplication gain in a linear mode, using UV illumination. In Geiger-mode operation at room temperature with gated quenching, no after-pulsing effect was observed up to 100 kHz. The single-photon detection efficiency and dark-count probability were measured to be ${sim}$1% and ${sim} 3times 10^{- 2}$ at 265 nm, respectively.      

GaN基雪崩光电二极管及其研究进展

越来越多的民用与军事对高灵敏度紫外探测的需求促进了GaN基雪崩光电二极管（APD）的快速发展。雪崩光电二极管工作在高反偏电压状态,器件内部载流子在高场下发生碰撞离化,从而使探测信号产生增益。首先对GaN基雪崩光电二极管的研究进展进行了回顾,然后重点报道了器件的增益最大可达3105,介绍了本征层厚度与器件暗电流的关系,简单介绍了正在组建的基于相敏探测的交流增益测试系统,并研究了过剩噪声与调制频率之间的关系,发现在低频波段（30~2kHz）,过剩噪声呈现1/f噪声特性。最后,对盖革模式的雪崩光电二极管的研究进展及应用前景进行了简单介绍。     

High-speed InP/InGaAsP/InGaAs avalanche photodiodes grown bychemical beam epitaxy

High-performance InP/InGaAsP/InGaAs avalanche photodiodes (APDs) grown by chemical beam epitaxy are described. These APDs exhibit low dark current (less than 50 nA at 90% of breakdown), good external quantum efficiency (greater than 90% at a wavelength of 1.3 μm), and high avalanche gain (≃40). In the low-gain regime, bandwidths as high as 8 GHz have been achieved. At higher gains, a gain-bandwidth-limited response is observed; the gain-bandwidth product is 70 GHz     

Double Mesa Sidewall Silicon Carbide Avalanche Photodiode

We report a double mesa 4H-SiC avalanche photodiode (APD) that suppresses premature edge break-down. The motivation for the double mesa structure is to eliminate the optically dead region that extends radially up to 30 $mu{hbox {m}}$ beyond the active region of conventional beveled mesa SiC APDs, which can significantly restrict the fill-factor of arrays.      

Avalanche Noise Characteristics in Submicron InP Diodes

We report excess noise factors measured on a series of InP diodes with varying avalanche region thickness, covering a wide electric field range from 180 to 850 kV/cm. The increased significance of dead space in diodes with thin avalanche region thickness decreases the excess noise. An excess noise factor of F = 3.5 at multiplication factor M = 10 was measured, the lowest value reported so far for InP. The electric field dependence of impact ionization coefficients and threshold energies in InP have been determined using a non-local model to take into account the dead space effects. This work suggests that further optimization of InP separate absorption multiplication avalanche photodiodes (SAM APDs) could result in a noise performance comparable to InAlAs SAM APDs.     

Experimental Determination of the Gain Distribution of an Avalanche Photodiode at Low Gains

A measurement system for determining the gain distributions of avalanche photodiodes (APDs) in a low gain range is presented. The system is based on an ultralow-noise charge-sensitive amplifier and detects the output carriers from an APD. The noise of the charge-sensitive amplifier is as low as 4.2 electrons at a sampling rate of 200 Hz. The gain distribution of a commercial Si APD with low average gains is presented, demonstrating the McIntyre theory in the low gain range.      

High Detection Sensitivity of Ultraviolet 4H-SiC Avalanche Photodiodes

We report 4H-SiC p-i-n avalanche photodiodes (APDs) with very low dark current. When biased for a photocurrent gain M of 1000, a 100-mum-diameter device exhibits dark current of 5 pA (63 nA/cm²), corresponding to primary multiplied dark current of 5 fA (63 pA/cm²). The peak responsivity at unity gain is 93 mA/W (external quantum efficiency = 41%) at lambda = 280 nm. The excess noise factor corresponds to k = 0.1. Detection of several tens of femtowatts of ultraviolet light is reported.     

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     

Effect of impact ionization in the InGaAs absorber on excess noise of avalanche photodiodes

The effects of impact ionization in the InGaAs absorption layer on the multiplication, excess noise and breakdown voltage are modeled for avalanche photodiodes (APDs), both with InP and with InAlAs multiplication regions. The calculations allow for dead space effects and for the low field electron ionization observed in InGaAs. The results confirm that impact ionization in the InGaAs absorption layer increases the excess noise in InP APDs and that the effect imposes tight constraints on the doping of the charge control layer if avalanche noise is to be minimized. However, the excess noise of InAlAs APDs is predicted to be reduced by impact ionization in the InGaAs layer. Furthermore the breakdown voltage of InAlAs APDs is less sensitive to ionization in the InGaAs layer and these results increase tolerance to doping variations in the field control layer.