Voxtel Blog

Discrimination of Photon- and Dark-Initiated Signals in Multiple Gaine Stage APD Photoreceivers

May 13, 2013

The IEEE Transactions on Electron Devices has accepted another paper authored by Voxtel staff for publication. The newest paper, “Discrimination of Photon- and Dark-Initiated Signals in Multiple Gain Stage APD Photoreceivers,” describes the different count distributions and statistical properties of photon-initiated avalanche events and dark current-initiated avalanche events. The paper shows that in Voxtel’s single-carrier multiplication (SCM) avalanche photodiode (APD), there is an ability to discriminate one from the other. The paper describes the numeric and analytical models that can be used to model these events in a photoreceiver.

A pre-publication version of the paper is available here.

The complete abstract follows:

We demonstrate the ability of linear mode single carrier multiplication (SCM) avalanche photodiode (APD) -based optical receivers to discriminate single-photon-initiated avalanche events from dark-current-initiated events. Because of their random spatial origin in discrete regions of the depletion region, in the SCM APD the dark-generated carriers multiply differently than the photon-generated carriers. This causes different count distributions and necessitates different statistical descriptions of the signal contributions from photon- and dark-originating impulse responses. To include dark carriers in the performance models of the SCM APD, we considered the influence of the spatial origin of the ionization chains on a receiver’s noise performance over the times the optical pulse is integrated by the receiver’s decision circuits. We compare instantaneous (time-resolved) numeric and pseudo-DC analytical models to measured SCM APD data. It is shown that it is necessary to consider both the distribution of spatial origin and the instantaneous properties of the ionization chains to describe statistically an SCM APD receiver. The ability of SCM APD receivers to discriminate single photon events from single dark events is demonstrated, and the effective gain and excess noise contributions of the light- and dark-initiated avalanche events and their influence on receiver sensitivity and signal-to-noise characteristics is shown.

Photonics Online Interviews Voxtel at SPIE Defense, Security and Sensing Exposition

May 7, 2013

If you weren’t able to visit with Voxtel last week at the SPIE Defense, Security and Sensing Exposition, you can still learn what’s new.  Voxtel Vice President of Business Development Joe LaChapelle met with Photonics Online during the exposition to discuss Voxtel’s latest power- and cost-saving technology, including the ROX™ line of avalanche photodiode (APD) laser rangefinder (LRF) receivers, the Metolius™ line of high-quantum efficiency (HQE) p-i-n (PIN) photodiodes, and a 64-channel time-to-digital converter.

To watch the interview with Joe and to learn how Voxtel technology can reduce the cost of high-performance military and medical imaging systems, click here.

This Week at SPIE Defense, Security and Sensing: Meet Voxtel Leaders, Learn About Voxtel Tech

April 30, 2013

This week, Voxtel is exhibiting a new ROX™ Laser Rangefinder (LRF) receiver and multi-channel time-to-digital counter (TDC) at SPIE Defense, Security and Sensing 2013, the premier scientific conference for optics, imaging, and sensing in defense, security, industry and the environment.

To meet Voxtel’s leaders and to learn how these technologies can improve the performance and reduce the cost of legacy systems, visit us at booth 2048, April 30 through May 2, Baltimore Convention Center, Baltimore, Md.

Voxtel paper verifies that SCM APDs can be described by superlattice and staircase APD models from the 80s.

April 17, 2013

The IEEE Transactions on Electron Devices has accepted for publication a paper authored by George Williams, Madison Compton, and Andrew Huntington of Voxtel titled Multi-gain-stage InGaAs Avalanche Photodiode with Enhanced Gain and Reduced Excess Noise. The paper describes the device architecture and DC performance characteristics of Voxtel’s single carrier multiplication (SCM) avalanche photodiode (APD) technology, and provides measured data and numerical models, which verify that the SCM APD can be described, analytically, by models developed in the 1980s to describe superlattice and staircase APDs.

A pre-publication version of the paper is available here.

The complete abstract follows:

We report the design, fabrication, and test of an InGaAs avalanche photodiode (APD) for 950-1650 nm wavelength sensing applications. The APD is grown by molecular beam epitaxy on InP substrates from lattice-matched InGaAs and InAlAs alloys. Avalanche multiplication inside the APD occurs in a series of asymmetric gain stages whose layer ordering acts to enhance the rate of electron-initiated impact ionization and to suppress the rate of hole-initiated ionization when operated at low gain. The multiplication stages are cascaded in series, interposed with carrier relaxation layers in which the electric field is low, preventing avalanche feedback between stages. These measures result in much lower excess multiplication noise – and stable linear-mode operation at much higher avalanche gain – than is characteristic of APDs fabricated from the same semiconductor alloys in bulk. The noise suppression mechanism is analyzed by simulations of impact ionization spatial distribution and gain statistics, and measurements on APDs implementing the design are presented. The devices employing this design are demonstrated to operate at linear-mode gain in excess of 6,000 without avalanche breakdown. Excess noise characterized by an effective impact ionization rate ratio below 0.04 were measured at gains over 1,000.



Non-local Model for the Spacial Distribution of Impact Ionization Events in Avalanche Photodiodes

April 11, 2013

Voxtel staff have co-authored a paper with the University of New Mexico titled Non-local Model for the Spatial Distribution of Impact Ionization Events in Avalanche Photodiodes. The paper describes the numeric models developed by University of New Mexico to describe the performance of Voxtel’s single carrier multiplication (SCM) APD. The paper has been submitted for publication to Applied Physics Letters (APL).

The complete abstract follows:

We report an extension of the analytical Dead Space Multiplication Theory [IEEE Trans. Electr. Dev., vol. 39, pp. 546-552, 1992] that provides the means to analytically determine the spatial distribution of electron and hole impact-ionization events in an arbitrarily specified heterojunction multiplication region. The model can be used to understand the role of dead space in regularizing the locations of impact ionization. It can also be utilized to analyze, design and optimize new generations of ultra-low noise, multi-staged gain avalanche photodiodes based upon judiciously energizing and relaxing carriers to enhance electron impact ionizations and suppress hole impact ionizations.

Voxtel Paper Published in Journal of Applied Physics

April 9, 2013

The Journal of Applied Physics has published a paper authored by Voxtel staff titled Time resolved gain and excess noise properties of InGaAs/InAlAs avalanche photodiodes with cascaded discrete gain layer multiplication regionsThe paper, co-authored with contributors from the University of New Mexico, discusses the temporal properties of the count distributions and low order statistical moments of an APD avalanche buildup process. The high gain of Voxtel’s single carrier multiplication (SCM) APDs allow for a convenient platform to investigate APD properties over the times of the impulse response where pulse detection is performed. The paper shows that the traditional McIntyre equation often used to model APD performance is inadequate for describing photoreceiver performance. The paper also shows the performance benefits of Voxtel’s SCM APD technology compared to conventional APD technology.

The paper is free of charge from the Journal of Applied Physics  (http://jap.aip.org/resource/1/japiau/v113/i9/p093705_s1?isAuthorized=no&view=print)

This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in the Journal of Applied Physics, vol. 113, Mar. 2013 and may be found at http://jap.aip.org/resource/1/japiau/v113/i9/p093705_s1?isAuthorized=no&view=print.

The complete abstract is below

To predict pulse detection performance when implemented in high speed photoreceivers, temporally resolved measurements of a 10-stage InAlAs/InGaAs single carrier multiplication (SCM) avalanche photodiode (APD)’s avalanche response to short multi-photon laser pulses were explained using instantaneous (time resolved) pulse height statistics of the device’s impulse response. Numeric models of the junction carrier populations as a function of the time following injection of a primary photo-electron were used to create the probability density functions (pdfs) of the instances of the avalanche buildup process. The numeric pdfs were used to generate low frequency gain and excess noise models, which were in good agreement with analytic models of multiple discrete low-gain-stage APDs and with measured excess noise data. The numeric models were then used to generate the instantaneous and cumulative instantaneous low order statistics of the instances of the impulse response. It is shown that during the early times of the impulse response, the SCM APDs have lower excess noise than the pseudo-DC measurements and the common APD models used to describe them. The methods of determining the time resolved low order statistics of APDs are described and the importance of using time-resolved models of APD gain and noise is discussed.

© 2013 American Institute of Physics

Voxtel Awarded DARPA Contract

January 10, 2012

Voxtel has been awarded a 9 month contract by DARPA under the MGRIN-II program to develop ink jet printed (IJP) gradient index optics. The work, which will be conducted in partnership with the University of Oregon, leverages Voxtel’s leadership position in nanocrystal fabrication, solid state chemistry, and ink jet printed devices. The new GRIN fabrication technology lends itself naturally to flexible and inexpensive manufacturing techniques, and Voxtel’s IJP manufacturing capability while advancing GRIN lens design and fabrication technology.