Dark current behaviors of the 2.6 μm cutoff wavelength In0.83Ga0.17As photodetectors are investigated as a function of the mesa etching depth. The total dark current monotonically declines from 2.0×10-6 A/cm2 to 8.3×10-7 A/cm2 at 180 K and -10 mV as the mesa etching depth decreases from 2.6 to 0.9 μm. Meanwhile, an order of magnitude lower surface leakage current from 4.56 to 0.47 nA/cm, and a narrower statistical distribution are observed simultaneously. Moreover, the 300 K peak detectivity and quantum efficiency increase from 2.6×1011 to 5.4×1011 cmHz1/2/W and from 67.1% to 71.2%, respectively, as the mesa etching depth decreases from 2.6 to 0.9 μm, benefit from the lateral carrier collection effect. These results suggest shallow mesa structures are indispensable towards surface leakage free In0.83Ga0.17As photodetectors.

In _0.75 Ga _0.25 As and In _0.83 Ga _0.17 As 320×256 short-wave infrared focal plane arrays (SWIR FPAs) with pixel pitches of 24 and 30 μm, extended cutoff wavelengths of 2.2 and 2.5 μm, low dark current densities of 5.2 and 21 nA/cm ² , and high peak detectivities of 6×10 ¹¹ and 6×10 ¹² cmHz ^1/2 W ⁻¹ are attained at 180 K, respectively. Lower 1/f noises and smaller knee frequencies are observed for the 2.2 μm FPA, indicates the dislocation defect-related trap states act as the major contributor for the 1/f noise. The non-uniformities of the dark signal and the dark noise are roughly the same for both FPAs at a short integration time of 1 ms (29% and 25% at 180 K, respectively) whereas are much smaller for the 2.2 μm FPA at longer integration times. Moreover, the dark current shot noise dominant integration time ranges are determined to be >20 and >2 ms for the 2.2 and 2.5 μm FPAs, respectively. Enhanced heat signature recording capability is also observed for wider SWIR spectral range while more effective suppression routes of dislocation defect must be incorporated for further improved sensitivity.

By incorporating of a combined mesa cleaning of SF6 plasma bombarding and HCl rinsing prior to the SiNx passivation, an ultra-low dark current density of 9.1 nA/cm2 at 180 K under a reverse bias of -10 mV for 30 μm pitch In0:83Ga0:17As focal plane arrays (FPAs) with an extended cutoff wavelength of 2.6 μm has been achieved. Six times higher dynamic differential resistance-area product of 35 Ω · cm at 300 K and increased activation energies for dark current were also attained in comparison to reference FPAs. Shockley-Read-Hall lifetimes of ∼40 and ∼200 ns at 300 and 180 K were determined from theoretical simulation analyses, respectively. These results suggest such methods effectively remove the low resistance leakage pathways on the micro-mesa sidewall surfaces, and are essential for large format and high fill-factor FPAs with negligible surface leakage current.

Geiger-mode InGaAsP/InP single photon avalanche photodiode (SPAD) with a low dark count rate (DCR) of 870 Hz at a photon detection efficiency (PDE) of 20% at 1064 nm is achieved for a 40 micron diameter device at −30 °C. Extensively optimized and accurately controlled shallow/deep two-step pn junction and doping profiles are identified to play decisive roles for the performance improvement. While a state-of-the-art specific detectivity of 1.4×10 ¹⁴ cm·Hz ^1/2 /W is realized for the optimized SPAD, a temperature coefficient of the breakdown voltage (V _br ) of 139 mV/K, a dark current of 200 pA at 90%V _br and a timing jitter of 280 ps at 20% PDE are also simultaneously attained. Thermal activation energies of approximate 0.5 eV are observed for both the dark current and the DCR at 253–293 K, indicates the dominant source of dark carriers is the mid-gap defect trapping states-related tunneling in the InGaAsP absorber.

The dark current and the photo response characteristics of extended wavelength In _0.83 Ga _0.17 As/InP photodetectors (PDs) with n-In _0.83 Ga _0.17 As absorber doped to 8×10 ¹⁵ , 7×10 ¹⁶ and 1×10 ¹⁷ cm ^-3 are investigated in an elevated temperature range of -40 to 100°C. The lightly doped PD exhibits a lower (higher) dark current than the heavily doped PD at temperatures higher (lower) than 30°C. The photocurrent, the spectral responsivity and the blackbody response voltage for the heavily doped PD rapidly decrease at temperatures higher than 30°C, while remain almost unchanged until 90°C for the lightly doped PD. The trend of the intermediately doped PD is between the two. In contrast, a consistently increasing trend of the dark noise over the whole measured temperature range are observed for three PDs. Theoretical calculations indicate such behaviors are essentially related with the temperature-dependent variation of the Shockley-Read-Hall lifetimes under different doping concentration.

Performances of In_0.75Ga_0.25As focal plane arrays (FPAs) with an extended cutoff wavelength of 2.2 μm are remarkably improved by largely increasing the overshooting composition of the linearly-grading In_xAl_1-xAs buffer layer. Zinc-diffused planar 640×488 FPAs with a pixel pitch of 23 μm are fabricated on both the regular and the large overshooting epi-wafers with x=0.77 and x=0.85 for the end compositions of the linearly-grading In_xAl_1-xAs, respectively. An order of magnitude lower dark current density of 1.1×10^-10 A/cm² is achieved at 150 K for the large overshooting FPAs when comparing with 2.1×10^-9 A/cm² for the regular FPAs. Suppressed dark signal and dark noise voltages are observed simultaneously over the measured whole integration time range. Moreover, the measured non-uniformity of the light response signal voltage drastically dropped from 16.4% to 2.9% while the peak detectivity substantially jumped from 7.1×10¹² to 1.8×10¹³ cmHz^1/2W^-1. A signal to noise ratio enhanced laboratory imaging demonstration is also provided. These results suggest the large overshooting epitaxial technology can serve as a highly viable route for the lattice-mismatched In_xGa_1-xAs FPAs towards further performance enhancement.