Development of low excess noise infrared avalanche photodiodes incorporating InAs and AlInAsSb

Detection of infrared photons beyond 1.1 μm requires narrow-bandgap semicon-
ductors, as silicon is insensitive to longer wavelengths. Indium Arsenide (InAs)
responds to light up to ≈ 3.5 μm at room temperature, suiting it to mid-wave
infrared (MWIR) sensing. InAs also provides internal gain via impact ionisation,
with its strongly asymmetric ionisation coefficients driving an electron-initiated
avalanche and a gain-independent bandwidth distinguishing InAs detectors as
electron APDs (e-APDs), a class of highly sensitive detectors for photon-starved
applications.
Wide bandgap quaternary Al0.8In0.2As0.31Sb0.69 grown on InAs is explored as
a protective and passivation layer for planar InAs APDs. The APDs showed
stable dark current at room temperature, with no drift over 2+ hours at high bias.
Bulk-dominated InAs APDs were demonstrated scaling down to 25 μm2 at room
temperature, with activation energy of 0.36 eV, close to the InAs bandgap, indicat-
ing high-quality InAs layers. The first excess noise report of planar InAs APDs
across 9 pixels exhibiting a sub-2 excess noise factor is demonstrated. Crosstalk
characterisation showed a lower peripheral response when the neighbouring pixels
were under bias, indicating the need for guard rings to suppress crosstalk.
The properties of the wide bandgap Al0.8In0.2As0.31Sb0.69 grown on an InAs
substrate were investigated as an avalanche layer through a complementary pair of
p-i-n and n-i-p wafers. The p-i-n diodes show an extremely low excess noise factor
(F ) < 0.03 and high avalanche multiplication (M ) > 100 at room temperature,
contrary to the n-i-p diodes’ F > 17 at M ≈ 3. Therefore, Al0.8In0.2As0.31Sb0.69
can be paired with an InAs absorber in a separate absorption and multiplication
avalanche photodiode to detect MWIR.
Finally, packaged and cooled planar InAs APDs were used in long-wavelength
detection. Low optical powers in the picowatt range were detected from 2.3 μm
to 3.4 μm. Timing jitter and simple LiDAR experiments using InAs APDs show
timing jitter of 38–45 picoseconds at 3.1 μm, capable of resolving features at 6.6 mm
depth. Low-temperature characterisation of Al0.8In0.2As0.31Sb0.69 suggests poorer
silicon activation at lower temperatures.