High-performance resonant-cavity photodetectors

To suppress the electric field crowding at sidewall and improve the detection sensitivity of the AlGaN separate absorption and multiplication (SAM) avalanche photodiodes (APDs), we propose the new AlGaN APDs structure combining a large-area mesa with a field plate (FP). The simulated results show that the proposed AlGaN APDs exhibit a significant increase in avalanche gain, about two orders of magnitude, compared to their counterparts without FP structure, which is attributed to the suppression of electric field crowding at sidewall of multiplication layer and the reduction of the maximum electric field at the p-type GaN sidewall in p–n depletion region. Meanwhile, the APDs can produce an obviously enhanced photocurrent due to the increase in cross sectional area of multiplication region.

A particular system for excess noise of avalanche photodiode (APD) measurement was build. Then the signal-noise ratio at different reverse voltage and the noise spectrum are measured and analyzed on different devices. First, the noise measurement system was constructed to fulfill the requirement that a high DC voltage can be applied on, and the measurement system was carefully shielded to protect from disturbance of electromagnetic radiations. Than we measured the noise spectrums of separate absorption and multiplication (SAM) type solar-blind APDs. The noise spectrums of SAM APDs which have different dark current levels were also measured. The results show that the low-frequency noise is dominant across a wide frequency range. And as the dark current goes higher, shot noise and low-frequency noise go higher at the same time. And the low-frequency noise will also takes more proportion in the spectrum when dark current goes higher. On the other hand, noise measurements at different reverse voltage and in either UV illumination or dark show that the excess noise factor increase faster as the gain increase. This leads to a decrease of signal-noise ratio at very high gain. In order to get a higher signal-noise ratio, a proper high gain should be adopted, rather than a gain “higher and better”.

Digital alloy (DA) InAlAs on the InP substrate exhibits a lower excess noise compared to a traditional In0.52Al0.48As random alloy as the multiplication layer in avalanche photodiodes (APDs). This work implements DA InAlAs as the multiplication layer in a 1550 nm separate absorption, grading, charge, and multiplication APD and characterizes the performances through various analyses. The device reaches a maximum gain of 221 before avalanche breakdown, with a maximum gain-bandwidth product of more than 140 GHz. At 90% breakdown voltage, the dark current density is 4.1 mA/cm2, and the responsivity is 0.48 A/W at unit gain. Excess noise factors were identified, yielding an effective k value of around 0.15, which is lower than that of random alloy In0.52Al0.48As APDs (k ∼0.2). These findings show that DA InAlAs has the potential to be a promising material for high-performance APDs.

The detailed procedure of modeling spectral responsivity characteristics for separate absorption and multiplication (SAM) $$\hbox {GaN/Al}_{0.15}\hbox {Ga}_{0.85}\hbox {N}$$ avalanche photodiode (APD) is presented. In order to verify the validity of numerical models, the photoresponse spectra under different biases are first shown. It is found that a window region with wavelength range from 330 to 360 nm is formed regardless of reverse bias, and the responsivities with wavelength range from 240 to 380 nm notably increase with bias. The role of n-type AlGaN layer in the photoresponse mechanism is then primarily studied. Our discussion focuses on the dependence of responsivity on the thickness and doping concentration of n-type layer, respectively. It is demonstrated that the rejection ratio of the detector increases exponentially with the thickness of n-type layer as long as its thickness exceeds 50 nm. Finally, the optimal doping concentration of n-type layer is obtained for optimizing SAM GaN/AlGaN APD.

In this communication, the potentiality of InSb material as an avalanche photodiode (APD) device is investigated. Current density-voltage (J-V) characteristics at 77K of InSb pin photodiodes were simulated by using ATLAS software from SILVACO, in dark conditions and under illumination. In order to validate parameter values used for the modeling, theoretical J-V results were compared with experimental measurements performed on InSb diodes fabricated by molecular beam epitaxy. Next, assuming a multiplication process only induced by the electrons (e-APD), different designs of separate absorption and multiplication (SAM) APD structure were theoretically investigated and the first InSb SAM APD structure with 1μm thick multiplication layer was then fabricated and characterized.

A model for the jitter of avalanche photodiodes with separate absorption and multiplication regions

In this work, solar-blind UV 4H-SiC avalanche photodetectors were fabricated and tested in linear and Geiger modes. APDs with both PIN and separate absorption and multiplication (SAM) structures were investigated. PIN structures demonstrated higher quantum efficiencies while the SAM structure exhibit lower leakage currents. Deposition of a thin film optical filter on top of the devices was used to provide a high photon rejection ratio of (Stas add value here). However, an external filter showed a better photon rejection ratio compared to the deposited one by about one order of magnitude.

Waveguide-coupled Ge/Si separate absorption, charge and multiplication avalanche photodiodes (SACM APDs) have shown significant potential as high-sensitivity, low-noise, and high-speed photo-detection for optical communications. Here we present a nanoscale single-mode waveguide-integrated vertical Ge absorption, lateral Si charge and single multiplication configuration for a waveguide Ge/Si SACM APD. This device can achieve 90% absorption at 1550 nm wavelengths with a 10 μm-long Ge layer. The device exhibits a seven times reduction in device length compared to conventional waveguide structures and a 29% increase compared to multi-mode interference coupling. Meanwhile, a 3-dB bandwidth can achieve 47 GHz, which is five times higher than the conventional vertical Ge absorption, lateral Si charge and multiplication devices.

In this paper, a new high optical gain amorphous avalanche photodiode has been successfully fabricated on ITO/glass substrate by plasma enhanced chemical vapor deposition (PECVD). All of these superlattice (SL) structures are made of an a-Si/SiC:H heterojunction to spatially confine the carrier ionization events within the narrow bandgap material (a-Si:H). As the carriers move across the heterobarrier step, they gain kinetic energy from the band edge discontinuity thus effectively reducing the impact ionization threshold energy. In this way each carrier will impact ionize a new electron-hole pair and the ionization rate can be enhanced. The performance of high gain, high sensitivity and low noise can be achieved. Due to the multiplication mechanism in the Si/SiC:H layer, the optical gain will be enhanced. For the a-SiC:H graded-gap superlattice structure, the room-temperature electron and hole impact ionization rates, α and β, have been determined by the photocurrent multiplication measurements. The ratio of the electron to hole ionization rates is 7.743 at a fixed electric field of 2.19×10^5Vcm^(-1). Avalanche multiplication in the superlattice layer yields a high optical gain of 206 at a reverse bias V(subscript R)=20V and an incident light power P(subscript in)=5μW and has a switching time of 7.2μs at a load resistance R(subscript L)=2.2KΩ. Multiplication excess noise is also measured, and is used to evaluate the ionization rate ratio. It was found that the a-SiC:H graded-gap superlattice avalanche photodiode generates high optical gain and low excess noise during the photocurrent multiplication. These results indicate that the a-SiC:H graded-gap superlattice avalanche photodiode is a promising device for the high sensitive imaging sensor. Besides, a variety of peak response wavelength is achievable by changing the applied bias and the well width in the SL structure, making the device useful as a wavelength selective multimedia color management photosensor.

We demonstrate a separate absorption, charge and multiplication (SACM) avalanche photodiode (APD) on silicon nitride (Si₃N₄) waveguide using an adhesive die-to-wafer bonding technique. Our heterogeneous APDs have a low dark current of 10 nA at -27 V. A 120 μm long APD has 77% internal quantum efficiency at unity gain, and a responsivity of 14 A/W at -29 V for -11.9 dBm input optical power at 1550 nm wavelength.

High-performance waveguide-integrated Ge/Si APDs in separate absorption, charge, and multiplication (SACM) schemes have been exploited to facilitate energy-efficient optical communication and interconnects. However, the charge layer design is complex and time-consuming. A waveguide-integrated Ge/Si avalanche photodetector (APD) is proposed in a separate absorption and multiplication (SAM) configuration. The device can work at low voltage and high speed with a lateral multiplication region without complexity of the charge layer. The proposed device is implemented by the complementary metal-oxide-semiconductor (CMOS) process in the 8-inch Si photonics platform. The device has a low breakdown voltage of 12 V and shows high responsivity of 15.1 A/W at 1550 nm wavelength under optical power of −22.49 dBm, corresponding to a multiplication gain of 18.1. Moreover, an opto-electrical bandwidth of 20.7 GHz is measured at 10.6 V. The high-speed performance at low voltage shows a great potential to implement high-energy-efficient Si optical communications and interconnections.

We report separate absorption, charge, and multiplication (SACM) avalanche photodiodes (APDs) in the Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> As <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</sub> Sb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-y</sub> material system for 2-μm detection. Gain, dark current, and low excess noise are demonstrated.

A general theory of noise in avalanche photodiodes (APDs), photomultipliers, and other cascaded multiplication devices in which ionization is independent of a carrier's history is presented. The theory is based on a composition law that allows the calculation of the gain distribution of a multilayer structure from the known distributions for each layer. The composition law is used to establish some well-known results and a number of new results. New formulas are derived for the gain and excess noise of a general double-carrier structure composed of multiple identical stages. A set of differential equations is derived for the case of continuous multiplication, as in a conventional APD. New results are reported for the noise of the staircase APD and for an APD with two regions of constant but different ionization ratios. The latter can be used to model the InGaAs/InP separated absorption and multiplication APD.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

We present the detailed procedure for modeling of separate absorption and multiplication (SAM) GaN/AlGaN avalanche photodiode (APD). The bias-dependent spectral responsivity characteristics are obtained by using the constructed two-dimensional numerical model. It is found that the spectral responsivities with wavelength from 240 to 450nm are entirely increased with the increased bias.

InP/InGaAs avalanche photodiodes with separate absorption and multiplication regions (SAM APD's) have been fabricated from wafers grown by atmospheric-pressure metalorganic chemical vapor deposition. These APD's exhibit low dark current and good quantum efficiency. The pulse response exhibits the two-component response typical of the SAM-APD structure. The slow component is 6 ns and the fast component is 100 ps.