InP-based Avalanche Photodiodes Research Articles

High gain, low noise 1550 nm GaAsSb/AlGaAsSb avalanche photodiodes

High sensitivity avalanche photodiodes (APDs) operating at eye-safe infrared wavelengths (1400–1650 nm) are essential components in many communications and sensing systems. We report the demonstration of a room temperature, ultrahigh gain ( M = 278 , λ = 1550 n m , V = 69.5 V , T = 296 K ) linear mode APD on an InP substrate using a G a A s 0.5 S b 0.5 / A l 0.85 G a 0.15 A s 0.56 S b 0.44 separate absorption, charge, and multiplication (SACM) heterostructure. This represents ∼ 10 × gain improvement ( M = 278 ) over commercial, state-of-the-art InGaAs/InP-based APDs ( M ∼ 30 ) operating at 1550 nm. The excess noise factor is extremely low ( F < 3 ) at M = 70 , which is even lower than Si APDs. This design gives a quantum efficiency of 5935.3% at maximum gain. This SACM APD also shows an extremely low temperature breakdown sensitivity ( C b d ) of ∼ 11.83 m V / K , which is ∼ 10 × lower than equivalent InGaAs/InP commercial APDs. These major improvements in APD performance are likely to lead to their wide adoption in many photon-starved applications.

Study on surface leakage current at sidewall in InP-based avalanche photodiodes with mesa structure

A multi-mesa InGaAs/InP avalanche photodiode (APD) with the advantage of the completely restricted electric field is proposed. The surface defects, which are the reasons for the sidewall leakage current generation in the mesa-structure APD, are theoretically studied, and then a sidewall leakage current model is developed. The Silvaco Atlas device simulation tool is used to analyze the generation mechanism of the sidewall leakage current, and the effects of different mesa structures on the sidewall leakage current of the APD are compared. The simulation results show that the sidewall leakage current of the multi-mesa APD is about zero and is not affected by the terrace size, which can be contributed by a very weak electric field at the sidewall.

Characteristics of thin InAlAs digital alloy avalanche photodiodes.

InP-based avalanche photodiodes (APDs) are widely used in short-wave infrared (SWIR) communications. In this work, a thin (200 nm nominal) InAlAs digital alloy layer consisting of two monolayer (ML) InAs and two ML AlAs was grown on InP substrate and investigated in detail. APDs with p-i-n and n-i-p structures were fabricated and characterized. The current-voltage, capacitance-voltage characteristics, and excess noise were measured at room temperature with different laser wavelengths, and the measured effective k value (ratio of impact ionization coefficients) is about 0.15 with the multiplication gain up to 12. The randomly-generated path length (RPL) model was carried out to analyze the dead space effect. Our thin digital alloy successfully reduced excess noise compared with conventional In0.52Al0.48As random alloy without introducing new elements and shows the potential for high-speed, low noise APD applications.

Low-Noise 3-D Avalanche Photodiodes

In this paper, we present a new 3-D structure for the InP-based avalanche photodiode, aiming at decreasing the excess noise factor. To the best of our knowledge, it is the first time new device designs based on the recently developed 3-D spatial dead space model in 2014 have been proposed. In addition, we also propose a methodology, i.e., the 2-D planar absorption distribution projection technique, for further optimizing the 3-D model. According to our theoretical simulation results, by combining photonic crystal and selective area doping, the effective k values of InP and In0.52Al0.48As can be reduced to as low as ∼0.19 and as ∼0.13, respectively. Meanwhile, the optimal thickness of the multiplication region is larger than 0.45 $\mu\text{m}$ , which reduces the tunneling effect. The detailed parameter optimization process, including optics, electronics, and material, is comprehensively presented. The examples in this paper also provide a fresh idea for researchers to foretell and design new photodetectors with the 3-D structure.

On the Use of Gaussian Approximation in Analyzing the Performance of Optical Receivers

The analytical calculation of the bit error rate (BER) of digital optical receivers that employ avalanche photodiodes (APDs) is challenging due to 1) the stochastic nature of the avalanche photodiode's impulse-response function and 2) the presence of intersymbol interference (ISI). At ultrafast transmission rates, ISI becomes a dominant component of the BER, and its effect on the BER should be carefully addressed. One solution to this problem, termed the bit-pattern-dependent (PD) approach, is to first calculate the conditional BER given a specific bit pattern and then average over all possible bit patterns. Alternatively, a simplifying method, termed the bit-pattern-independent (PI) approach, has been commonly used whereby the average bit stream is used to calculate the distribution of the receiver output, which, in turn, is used to calculate the BER. However, when ISI is dominant, the PI approximation is inaccurate. Here, the two approaches are analytically compared by analyzing their asymptotic behavior and their bounds. Conditions are found to determine when the PI method overestimates the BER. The BER found using the PD method exponentially decays with the received optical power, whereas for the PI approach, the BER converges to a constant, which is unrealistic. For an InP-based APD receiver with a 100-nm multiplication layer, the PI method is found to be inaccurate for transmission rates beyond 20 Gb/s.

Study of Wasted Space Effect in Avalanche Photodiodes: A New Look at the Size-Dependent Impact Ionization Properties under Submicron Scale

Impact ionization is one of the most important behaviors for carrier transport in high-field region. In this paper, we study the size-dependent impact ionization coefficients induced by the distance that the carriers have to travel to leave out of the terminal of the multiplication layer after the last impact ionization event, which is defined as the “wasted space”. Monte Carlo method is carried out to calculate the size-dependent impact ionization coefficients under submicron scale, and to investigate the effect of wasted space. The conventional model of mean multiplication gain in avalanche photodiodes (APDs) is revised with the adoption of size-dependent impact ionization coefficients, and a good agreement is achieved in the device characteristics of multiplication gain of InP-based APD devices.

Arrays of InP-based Avalanche Photodiodes for Photon Counting

Arrays of InP-based avalanche photodiodes (APDs) with InGaAsP absorber regions have been fabricated and characterized in the Geiger mode for photon-counting applications. Measurements of APDs with InGaAsP absorbers optimized for 1.06 <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mu</i> m wavelength show dark count rates (DCRs) <20 kHz for room-temperature operation with photon detection efficiency (PDE) up to 50% and a reset or dead time of 1s. APDs with InGaAs absorbers optimized for 1.55 μm wavelength and 240 K temperature have DCRs <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&lt;</i> 20 kHz, PDE up to 45%, and a reset time of ~6 <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mu</i> s. Arrays for both wavelengths have been fabricated and packaged with GaP microlenses (of 100 and 50 μm pitch) and CMOS readout integrated circuits (ROICs). Comparisons are made between ROICs that operate in the framed-readout mode as well as those that operate in continuous-readout mode.

2.4 [micro sign]m cutoff wavelength avalanche photodiode on InP substrate

An InP-based avalanche photodiode with a cutoff wavelength of 2.4 µm is reported. Type-II GaInAs-GaAsSb quantum wells lattice-matched to InP were used in the absorption region of the photodiode for long-wavelength absorption. The device exhibited multiplication gain in excess of 30 at room temperature and in excess of 200 at 225 Kelvin with dark current density near breakdown of less than 0.66 mA/cm2.

Reliable non-Zn-diffused InP∕InGaAs avalanche photodiode with buried n-InP layer operated by electron injection mode

A new InP-based avalanche photodiode with a p-type neutral absorption layer and a buried n-contact has been developed. From the test results, it is confirmed that the device has good receiver performance, with a minimum sensitivity of −26.8 dBm at 10 Gbit/s, and sufficient reliability.

Failure mechanism of avalanche photodiodes in the presence of water vapor

Lower cost optoelectronic modules (transmitters and receivers) could be produced if components could operate reliably in a nonhermetic package. Experiments (operation in humid ambient as a function of temperature, relative humidity (RH), and voltage) were carried out on InP-based avalanche photodiodes (APDs). The objectives were to reveal any moisture-related failure modes, to understand the failure mechanisms, to determine the relevant acceleration factors, and to propose design or material modifications to prevent the failures. Leakage current vs. time was measured for nine cells of 20 devices each. All devices were examined by optical microscopy, and representative samples were studied by scanning electron microscopy. A failure mechanism related to corrosion of the passivating SiN and the underlying semiconductor was identified. Based on the voltage and RH dependence of the degradation rate, a model for the failure process was developed. The mechanism involves RH-dependent transport of charge across the surface of the SiN and Poole-Frenkel current flow through the SiN. This process eventually produces a short circuit.

Low avalanche noise characteristics in thin InP p/sup +/-i-n/sup +/ diodes with electron initiated multiplication

We have performed electron initiated avalanche noise measurements on a range of homojunction InP p/sup +/-i-n/sup +/ diodes with "i" region widths, w ranging from 2.40 to 0.24 μm. In contrast to McIntyre's noise model a significant reduction in the excess noise factor is observed with decreasing w at a constant multiplication in spite of /spl alpha/, the electron ionization coefficient being less than /spl beta/, the hole ionization coefficient. In the w=0.24 μm structure an effective /spl beta///spl alpha/ ratio of approximately 0.4 is deduced from the excess noise factor even when electrons initiate multiplication, suggesting that hole initiated multiplication is not always necessary for the lowest avalanche noise in InP-based avalanche photodiodes.