We demonstrate balanced InGaAs/InP single photon avalanche diodes (SPADs) operated in both pulse-gated mode and sinusoidal gating mode for data transmission rate up to 20 MHz. The photodiode pair is biased in a balanced configuration with only one of the SPADs illuminated. The common-mode signal cancellation realized with the balanced configuration enables detection of small avalanche pulses. Afterpulsing is significantly suppressed due to the capability of detecting small avalanche pulses at high laser repetition rate. For pulse-gated mode operation and laser repletion rate of 20 MHz at 240 K, the dark count probability for photon detection efficiency of 13% is 1.9×10-5. The afterpulse probability is 0.3% for 2 ns pulse width, hold off time of 20 ns, and 10% PDE, at 240K. For sinusoidal gating a phase shifter has been incorporated to achieve better synchronization between signals. At laser rate of 20 MHz and 240 K, the dark count probability and photon detection efficiency are 2.8×10-5 and 10.8% respectively.
Abstract—We demonstrate a sinusoidally-gated InGaAs/InP photodiode pair operated at wavelength of 1310 nm with high photon detection efficiency (PDE) and low dark count rate (DCR). The photodiode pair is biased in a balanced scenario so that the common component of the output signal is cancelled. The concept of balanced photodiodes helps improve detection efficiency while canceling the common mode signal, which, in this case, is the capacitive response of the photodiodes. In conventional sinusoidal gating, an extra component, – an RF filter (or several) at the gating frequency, is utilized to filter out the gating signal and leave the avalanche signal for detection. For this configuration, sinusoidally-gated counting systems are restricted to a single frequency. With the balanced single photon diodes (SPAD), sinusoidal gating within a continuous frequency range is feasible. A printed circuit with symmetric layout of two bias tees was fabricated on a duroid board to enable the application of AC and DC signals for the dual SPADs. At a laser repletion rate of 1 MHz and temperature of 240 K the DCR and PDE were 58 kHz and 43%, respectively. Afterpulsing probability was lower compared with a sinusoidually-gated single SPAD. Jitter of 240 ps was achieved with 1 photon per pulse for an excess bias of 1.6%.
There is a strong interest in developing sensitive Short Wavelength Infrared (SWIR) avalanche photodiodes (APDs) for
applications like eye safe laser ranging and robotic vision. The excess noise associated with the avalanche process is
critical in dictating the sensitivity of APDs. InGaAs APDs that are commonly used in the SWIR region have either InP
or InAlAs as an avalanche layer and these materials have excess noise factor of 0.5 and 0.22, respectively. Earlier,
Spectrolab had developed APDs with impact ionization engineering (I2E) structures based on InAlAs and InGaAlAs
heterostructures as avalanche layers. These I2E APDs showed an excess noise factor of 0.15. A photoreceiver based on
the I2E APD exhibited an noise equivalent power (NEP) of 150 fW/rt(Hz) over 1 GHz bandwidth at 1.06 μm. In this
paper, a new multiplier structure based on multiple stages of I2E is studied. The APDs show optical gains over 100
before device breakdown. The increased gain and low excess noise will improve the sensitivity of InGaAs APDs based
photoreceivers.
We report sinusoidal gating of InGaAs/InP single photon avalanche diodes (SPAD) operated
at wavelength of 1310 nm with high photon detection efficiency (PDE) and low dark count rate (DCR).
At a gating frequency of 80 MHz and temperature of 240 K the DCR and PDE were 15.5 kHz and 55%,
respectively. The slope of DCR versus PDE increases with higher laser repetition rate. There are two
mechanisms that contribute to this trend. The first is due to the lower afterpulse probability associated
with a lower laser repetition rate. The other is due to the RC effect, which is illustrated by an equivalent
circuit that includes a model of the SPAD. We also show that relative to gated passive quenching with
active reset (PQAR) for fixed PDE, sinusoidal gating yields lower afterpulsing rates for the same hold-off
time. This is explained in terms of the integrated pulse shape and the resultant charge flow. The afterpulse
probability, Pa, is related to the hold off time, T, through the power law, Pa∝T-α where α is a measure of the detrapping time in the multiplication region.
This paper describes single photon detection for Ge on Si separate-absorption-charge-multiplication (SACM) avalanche
photodiodes and advances in quenching for InP/InGaAs single photon avalanche diodes.
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