Separate Absorption, Grading, Charge, And Multiplication Research Articles

Material Defects and Dark Currents in InGaAs/InP Avalanche Photodiode Devices

An In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.53</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.47</sub> As/indium phosphide (InP) avalanche photodiode (APD) with a separate absorption, grading, charge, and multiplication (SAGCM) structure is epitaxially grown by molecular beam epitaxy (MBE). The resulting material is studied using X-ray diffraction (XRD), photoluminescence (PL), and scanning transmission electron microscopy. The activation energy extracted from the dark current of the APD indicates that it is dominated by the generation–recombination (G–R) process. Deep low-temperature PL peaks reveal the existence of an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}_{v} + 0.42$ </tex-math></inline-formula> -eV deep energy level defect in the indium–gallium–arsenide (InGaAs) absorber layer, which is considered to be a result of point defects caused by Ga-poor or In-poor MBE growth conditions. The effect of the defect on the dark current is confirmed using numerical calculation methods.

Simulation of Extended Wavelength Avalanche Photodiode with the Type-II Superlattice Absorption Layer

The relationship between the performance of avalanche photodiode (APD) and structural parameters of the absorption, grading, and multiplication layers has been thoroughly simulated and discussed using the equivalent materials approach and Crosslight software. Based on separate absorption, grading, charge, and multiplication (SAGCM) structure, the absorption layer of APD was replaced with InGaAs/GaAsSb superlattice compared to conventional InGaAs/InP SAGCM APD. The results indicated that the breakdown voltage increased with the doping concentration of the absorption layer. When the thickness of the multiplication layer increased from 0.1 μm to 0.6 μm, the linear range of punchthrough voltage increased from 16 V to 48 V, and the breakdown voltage decreased at first and then increased when the multiplication layer reached the critical thickness at 0.35 μm. The grading layer could not only slow down the hole carrier, but also adjust the electric field. The dark current was reduced to about 10 nA and the gain was over 100 when the APD was cooled to 240 K. The response wavelength APD could be extended to 2.8 μm by fine tuning the superlattice parameters. The simulation results indicated that the APD using superlattice materials has potential to achieve a long wavelength response, a high gain, and a low dark current.

Optimization of the Linearity of InGaAs/InAlAs SAGCM APDs

Linearity is of utmost importance for avalanche photodiodes (APDs) used in communication systems for Ethernet beyond 10 Gbit/s. APDs with high linearity are able to extend the transmission distance without additional power consumption, but the linearity has not been investigated in detail. In this paper, a model of the InGaAs/InAlAs separate absorption, grading, charge and multiplication (SAGCM) APD is established to optimize the linearity parameters in the device. The simulated results show that the grading layer and the charge layer are critical for the linearity and by reducing the thickness or the doping concentration of the grading layer, the linearity can be improved. Besides, a thick absorption layer improves the quantum efficiency while degrades the linearity. A thin multiplication layer improves the linearity.

Effect of Multiplication and Absorption Layers Width on Avalanche Multiplication Gain in InGaAs/InP Avalanche Photodiode

The separate absorption, grading, charge, and multiplication (SAGCM) InGaAs/InP avalanche photodiodes (ADPs) are widely used in long distance, high bit rate optical communication system due to their high performance and response to optical fiber wavelength spectrum. In this work, the effect of multiplication layer width (MLW) and absorption layer width (ALW) on APD performance is studied and investigated. Silvaco TCAD software is used as simulation tools to simulate a precise model of InGaAs/InP APD and analyze its, performance under an illuminated condition. As such, three different ALW with various MLW has been simulated while the structure values and material parameters are kept constant. It was found that in the APD with smaller MLW, the distance between the punch-through voltage and the breakdown voltage can be maximized. Therefore, the operation region of APD will be extended. In addition, the multiplication gain is obtained from the photocurrent and primary current by taking the APD collection efficiency effect under the consideration.

Fabrication and Characterization of Planar-Type Top-Illuminated InP-Based Avalanche Photodetector on Conductive Substrate with Operating Speeds Exceeding 10 Gbps

This paper presents a high-speed top-illuminated InP-based avalanche photodetector (APD) fabricated on conductive InP-wafer using planar processes. The proposed device was then evaluated in terms of DC and dynamic performance characteristics. The design is based on a separate absorption, grading, charge, and multiplication (SAGCM) epitaxial-structure. An electric field-profile of the SAGCM layers was derived from the epitaxial structure. The punch-through voltage of the SAGCM APD was controlled to within 16–17 V, whereas the breakdown voltage (VBR) was controlled to within 28–29 V. We obtained dark current of 2.99 nA, capacitance of 0.226 pF, and multiplication gain of 12, when the APD was biased at 0.9 VBR at room temperature. The frequency-response was characterized by comparing the calculated 3-dB cut-off modulation-frequency (f3-dB) and f3-dB values measured under various multiplication gains and modulated incident powers. The time-response of the APD was evaluated by deriving eye-diagrams at 0.9 VBR using pseudorandom non-return to zero codes with a length of 231-1 at 10–12.5 Gbps. There was a notable absence of intersymbol-interference, and the signals remained error-free at data-rates of up to 12.5 Gbps. The correlation between the rise-time and modulated-bandwidth demonstrate the suitability of the proposed SAGCM-APD chip for applications involving an optical-receiver at data-rates of >10 Gbps.

Digitally grown AlInAsSb for high gain separate absorption, grading, charge, and multiplication avalanche photodiodes

We report on the growth of high quality GaSb-based AlInAsSb quaternary alloy by molecular beam epitaxy (MBE) to fabricate avalanche photodiodes (APDs). By means of high resolution X-ray diffraction (HRXRD) and scanning transmission electron microscope (STEM), phase separation phenomenon of AlInAsSb random alloy with naturally occurring vertical superlattice configuration was demonstrated. To overcome the tendency for phase segregation while maintaining a highly crystalline film, a digital alloy technique with migration-enhanced epitaxy growth method was employed, using a shutter sequence of AlSb, AlAs, AlSb, Sb, In, InAs, In, Sb. AlInAsSb digital alloy has proved to be reproducible and consistent with single phase, showing sharp satellite peaks on HRXRD rocking curve and smooth surface morphology under atomic force microscopy (AFM). Using optimized digital alloy, AlInAsSb separate absorption, grading, charge, and multiplication (SAGCM) APD was grown and fabricated. At room temperature, the device showed high performance with low dark current density of ∼14.1 mA/cm2 at 95% breakdown and maximum stable gain before breakdown as high as ∼200, showing the potential for further applications in optoelectronic devices.

A Double Heterostructure Multiplication Region in AlGaN Based SAGCM Avalanche Photodiode

In this study, separate absorption, grading, charge, and multiplication (SAGCM) avalanche photodiode (APD) with double heterojunction AlN/AlxGa1-xN/GaN in multiplication region were designed to reduce excess noise using Monte Carlo simulation. The multiplication region was broken to three different regions and tried to enhance localization of the first and second impact ionization events at near the heterojunctions. The excess noise of the proposed structure, for high gains, was 64% smaller than that of the fabricated standard AlGaN-APDs.

Charge-layer design considerations in SAGCM InGaAs/InAlAs avalanche photodiodes

We report on the development of mesa-processed InGaAs/InAlAs avalanche photodiodes (APDs) for short-wave infrared (SWIR) imaging applications with demand for high gain and low breakdown voltage. Devices are designed with separate absorption, grading, charge, and multiplication (SAGCM) layers. Special attention has been paid to the charge layer in order to optimize the structure for low band discontinuities and an appropriate electric field distribution. Hereof, a combination of a p-type grading layer and charge layer is presented. Band-edge profile calculations as well as electro-optical characterization results of the APDs will be discussed in this article. Our optimized APD structures reveal low punch-through and low breakdown voltage of and , respectively. A maximum gain of in the linear operation mode is demonstrated at room temperature and has been measured at 20 V bias.

Experimental investigation of the charge-layer doping level in InGaAs/InAlAs avalanche photodiodes

We report on the development of mesa-processed InGaAs/InAlAs avalanche photodiodes (APDs) for short-wave infrared (SWIR) applications with demand for high gain and low breakdown voltage. Devices are designed with separate absorption, grading, charge and multiplication (SAGCM) layers. Special attention has been paid to the charge layer in order to optimize the distribution of the electric field across the device. Since the device performance significantly changes for deviations of only several percent in the doping concentration a series with variation of the charge-layer doping level has been carried out. Band-edge profile calculations as well as electro-optical characterization results of the APDs will be discussed in this article. Our optimized APD structures reveal a low dark-current density of Id=1×10-4A/cm2 at gain M=10 and a low breakdown voltage Vbd<30V. A maximum gain larger than 300 in the linear operation mode is demonstrated at room temperature as well as 140K.

A new model for avalanche build-up of carriers in a SAGCM avalanche photodiode

A new model for the avalanche build-up of carriers in an avalanche photodiode (APD) including the dead-space effect has been developed and used to study the frequency response of a resonant-cavity-enhanced (RCE) separate absorption, grading, charge, and multiplication (SAGCM) APD. In this model, the carriers are characterized by their energy and position in the region of multiplication. The excess energy of the carriers above threshold are assumed to be equally distributed among the carriers after impact ionization. The results are demonstrated with a In/sub 0.1/Ga/sub 0.9/As/Al/sub 0.2/Ga/sub 0.8/As RCE APD and good agreement was obtained from comparisons with the published experimental data for gain-bias and bandwidth-gain plots.

On the frequency response of a resonant-cavity-enhanced separate absorption, grading, charge, and multiplication avalanche photodiode

In this article the frequency response of a resonant-cavity-enhanced (RCE) separate absorption, grading, charge, and multiplication (SAGCM) avalanche photodiode (APD) has been investigated. This study on APDs includes the development of a model for the avalanche buildup of carriers including the dead-space effect. In this model, the carriers are characterized by their energy and position in the region of multiplication. The excess energy of the carriers above threshold are assumed to be equally distributed among the carriers after impact ionization. The analysis shown in this article can be used to study the frequency response of the APD for a wide range of reverse bias voltages. For low bias voltages, an analytical expression has been derived to study the emission of carriers from the interface trap. The delay due to diffusion of photogenerated carriers from the undepleted region of the absorption layer and the low velocity of carriers at low field have also been considered. The model is used to calculate gains at different biases and bandwidth at different dc gains. The results show good agreement with published experimental data on a RCE SA(G)CM APD.

An analytical approach to study the effect of carrier velocities on the gain and breakdown voltage of avalanche photodiodes

A simplified model for calculating gain and breakdown voltage of avalanche photodiodes (APDs) having constant ionization coefficients in their multiplication layer is presented. Good agreement is seen between the calculated results and the experimental data for published InP-InGaAs separate absorption, grading, charge, and multiplication (SAGCM) APDs. The model denotes that the gain and the breakdown voltage have a dependence on the carrier velocity ratio that is not predicted by conventional models. Hence, by comparing the calculated and measured static characteristics of the APD, one can estimate the velocity of minority carriers in the multiplication region of the device.

Two-dimensional gain profiles of InP/InGaAs separate absorption, grading, charge, and multiplication avalanche photodiodes modeled by a simplified stochastic approach

The two-dimensional (2D) gain profiles of InP/InGaAs separate absorption, grading, charge, and multiplication (SAGCM) avalanche photodiodes (APDs) have been modeled by using a simplified stochastic approach. The influence of the curved diffusion edge on the electric field in the periphery has been considered and electric field equations have been derived from the cylindrical Poisson’s equation. The electric field in the multiplication layer is significantly reduced when a partial charge sheet is incorporated in the device’s periphery. The modeled 2D gain profile for such a device agrees with experiment and demonstrates an effective suppression of the premature edge breakdown. These results and the uniformity issue of the 2D gain profiles are further discussed. From our analyses, we find that controlling the diffusion process within the p+ InP top layer and patterning the charge sheet mesa structure are most likely to affect the uniformity and symmetry of the 2D gain profiles for the InP/InGaAs SAGCM APDs.

Low-frequency noise in single growth planar separate absorption, grading, charge, and multiplication avalanche photodiodes

The current bias-dependence of low-frequency noise spectra in single growth planar separate absorption, grading, charge, and multiplication (SAGCM) APDs was studied. We have also investigated the influence of process variations on the noise spectra of the APDs. It was believed that devices processed with two types of processing (A and B) exhibited a lateral electric field component within the active area of the device. The process variations were clearly identified through the low-frequency noise performance of the devices. The decrease of the lateral component of an electric field within the active area of the device was correlated to changes in the device processing. It was found that a low temperature anneal of the device decreased the level of low-frequency noise in the devices processed with treatments B and C.

Modeling of two-dimensional gain profiles for InP-InGaAs avalanche photodiodes with a stochastic approach

The two-dimensional (2-D) gain profiles for separate absorption, grading, charge and multiplication (SAGCM) InP-InGaAs avalanche photodiodes (APD's) have been modeled with a stochastic approach. To consider the influence of the curved diffusion edge on the electric field within the periphery region, equations are derived from the cylindrical Poisson's equation. The electric field profiles are computed at various APD radii and the electric field in the multiplication layer is reduced significantly for APD's with a partial charge sheet in the periphery. It is demonstrated by the modeled 2-D gain profiles that the premature edge breakdown can be effectively suppressed for such devices. The modeled 2-D gain profiles for APD's with a partial charge sheet incorporated in the periphery are in good agreement with the experimental results. The results and the uniformity issue of the 2-D gain profiles are discussed. The effect of using curved diffusion interfaces instead of a steep mesa step is also explored; this suggests that the fabrication of a charge sheet mesa step may complicate the gain uniformity issue. From our analyses, we find that the uncertainty and the symmetry of both patterning the charge sheet mesa structure and controlling the diffusion interface between the p/sup +/ InP top layer and the n/sup -/ InP multiplication layer are most likely to affect the uniformity and the symmetry of the 2-D gain profiles for the SAGCM InP-InGaAs APD's.

Effect of mesa overgrowth on low-frequency noise in planar separate absorption, grading, charge, and multiplication avalanche photodiodes

The purpose of this paper is to present a detailed comparison of the low-frequency noise in single-growth and mesa overgrown planar separate absorption, grading, charge, and multiplication (SAGCM) avalanche photodiodes (APD's) passivated with SiN/sub x/. It was found that existing models did not explain the bias dependence of the low-frequency noise in the mesa overgrown devices. We have found that a low-temperature anneal decreased the low-frequency noise level in single-growth and mesa overgrown APD's. In addition, generation-recombination (G-R) noise was detected in mesa overgrown APD's.

A simplified approach to time-domain modeling of avalanche photodiodes

A simplified algorithm for calculating time response of avalanche photodiodes (APDs) is presented. The algorithm considers the time course of avalanche processes for the general case of position-dependent double-carrier multiplications including the dead space effect. The algorithm is based on a discrete time setting ideally suited for computer modeling and can be applied to any APD structure. It gives a fast and accurate estimation of the time and frequency response of APDs. As an example, the present method is applied to InP-InGaAs separate absorption, grading, charge, and multiplication (SAGCM) APDs. The variation of multiplication pain with bias voltage and 3-dB electrical bandwidth at different multiplication gain obtained using the new algorithm show good agreement with experimental results. The algorithm can be used to study temperature dependence of APD characteristics and can be easily extended to calculate the excess noise factor.

Low frequency noise in separate absorption, grading,chargeand multiplication (SAGCM) avalanche photodiodes

Low frequency noise spectra of five SAGCM APDs were measured. The experimental noise current spectra were fitted with S/sub I/=A/sub F/I/sub d//sup x//f/sup y/+2qI/sub d/M/sub eff/. Any enhancement in shot noise was included in M/sub eff/. The A/sub F/ factors were found to vary from 10/sup -7/ to 10/sup -5/ and were related to the I-V characteristics of these APDs.

Temperature dependence of breakdown voltages in separate absorption, grading, charge, and multiplication InP/InGaAs avalanche photodiodes

In this paper, we investigate temperature dependence of breakdown voltage V/sub br/ from -40 to 110/spl deg/C in separate absorption, grading, charge, and multiplication (SAGCM) InP/InGaAs avalanche photodiodes (APD's) with a range of device parameters. The experimental data shows that V/sub br/ is approximately a linear function of temperature, with a temperature coefficient /spl eta//sub exp/ between 0.13 and 0.16 V//spl deg/C. A physical model is developed and it demonstrates that V/sub br/ indeed varies linearly with temperature with a temperature coefficient /spl eta//sub the/ about 0.155 V//spl deg/C. It also explains successfully the small variation of /spl eta//sub exp/ among the APD's. Good agreement between the physical model predictions and experimental data of published InP-based APD's is also obtained. This good agreement demonstrates that the proposed physical model is appropriate to model the temperature dependent characteristics in any InP-based APD's. >

Multiplication in separate absorption, grading, charge, and multiplication InP-InGaAs avalanche photodiodes

Planar separate absorption, grading, charge, and multiplication (SAGCM) InP-InGaAs avalanche photodiodes (APD's) are ideal for studying the multiplication (photogain) versus bias voltage (M-V) characteristics. In this paper, the M-V characteristics-in SAGCM InP-InGaAs APD's are investigated both experimentally and theoretically. The self-calibrated nature of M and the bias-voltage independent quantum efficiency make it possible to compare theory and experiment accurately in an InP-based APD. The Miller empirical formula for Si and Ge is proved appropriate for the SAGCM InP-InGaAs APD's. Using a physics-based model, the M-V characteristics and its temperature dependence for all the SAGCM APD's with different device parameters is calculated theoretically, and the calculations are in good agreement to the experimental results. >