Jiaxiong Fang

GaInP–AlInP–GaAs Blue Photovoltaic Detectors With Narrow Response Wavelength Width

Ga_0.51In_0.49P-Al_0.52In_0.52In_0.48P-GaAs blue photovoltaic detectors using AlInP as a light absorption active layer and GaInP as a short wavelength limiting cap layer have been fabricated by using gas source molecular beam epitaxy, and their performances have been characterized in detail. Excellent performance has been demonstrated on the detectors, resistance area product of<i>R</i> ₀ <i>A</i> = 6.9 × 10⁸ ¿ · cm², and the open-circuit voltage of <i>V</i> _oc > 1.28 V have been measured at room temperature. The detectors show peak response at 480 nm with responsivity of 0.168 A/W at zero bias, as well as an inherent narrow wavelength width of 9.4%, which makes them a good candidate in blue light detection applications such as water related sensing and communication.

Impact of etching on the surface leakage generation in mesa-type InGaAs/InAlAs avalanche photodetectors

Effects of mesa etching and geometry on InGaAs/InAlAs avalanche photodiodes (APDs) were investigated by using both wet and inductively coupled plasma (ICP) etching with different mesa shapes as well as etchants. It was found that the mesa geometry had no evident impact on APDs characteristics regardless of the etching techniques applied. Besides, ICP-etched APDs showed faster punch-through, suppressed premature surface breakdown and lower dark current behaviors compared to the wet-etched devices. Substantially suppressed surface leakage was also observed for ICP-etched devices, showing 1 and 3 orders of magnitude better at room temperature and 77 K respectively, and over 1 order of magnitude higher surface resistivity up to 4×107 Ω cm, in comparison to the wet-etched APDs. Introduction of extra hydrogen and Ar plasma in ICP etching led to detrimental effects to APDs performance by enhancing the tunneling or recombination at surfaces. Those experimental results were clearly interpreted based on the surface state theories.

Study on dark current of extended wavelength InGaAs detectors

The short wavelength infrared (SWIR) band near 1.0-3.0μm plays an important role in many applications such as weather forecast, earth environmental or resource observation, low light level systems and astronomical observation. It is well known that InGaAs detectors can shift the cutoff wavelength from 1.7μm to 2.5μm with the higher fraction of indium in the ternary InXGa1-XAs material grown on InP, which results to material defects and poorer device characteristics due to the lattice mismatch. Dark current characteristics of extended wavelength InGaAs detectors were investigated in this paper. Dark current mechanisms for extended InGaAs detectors with different absorption layer parameters and device fabrication process were analyzed according to current-voltage curves at different temperatures and bias voltages. Activation energy of devices was extracted from current-voltage curves. Activation energy is related with absorption layer concentration and test temperature. Activation energy is the higher for the devices with the higher absorption layer concentration at lower bias voltage at the same temperature range, which shows that the narrower width of the depletion layer in the devices results to the lower generation-recombination current. The devices with the optimized etching and passivation parameters show higher thermal activation energy and the lower dark current. Dark current mechanisms of the ones are dominated by diffusion current at the higher temperature and lower bias voltage, whereas dominated by internal generation-recombination current and ohmic leakage current at the lower temperature.

Noise characteristics of short wavelength infrared InGaAs linear focal plane arrays

A noise characteristics model is presented for short wavelength infrared (SWIR) focal plane arrays (FPAs). The model shows the relationship between noise and varying integration time. The experimental results for different SWIR InGaAs linear FPAs in the 1.0–1.7u2009μm and 1.0–2.4u2009μm spectral range can be well fitted by this model. The noise of InGaAs FPAs with the conventional process in the 1.0–1.7u2009μm spectral range is determined by the shot noise from the photodiode, which provides a direction for reducing the noise of FPAs. The noise of InGaAs FPAs with the improved process in the 1.0–1.7u2009μm spectral range is determined by the noise from the readout integrated circuit (ROIC), which is due to the lower shot noise from the dark current of the photodiode. The noise of InGaAs FPAs in the 1.0–2.4u2009μm spectral range shows a transition from the fixed-pattern noise to the shot noise with a decrease of temperature as indicated by the model. This reduction is mainly due to the higher dark current of photodiodes and t...

Design of 800×2 low-noise readout circuit for near-infrared InGaAs focal plane array

InGaAs near-infrared (NIR) focal plane arrays (FPA) have important applications in space remote sensing. A design of 800×2 low-noise readout integrated circuit (T800 ROIC) with a pitch of 25 μm is presented for a dual-band monolithic InGaAs FPA. Mathematical analysis and transient noise simulations have been presented for predicting and lowering the noise in T800 ROIC. Thermal noise from input-stage amplifier which plays a dominant role in ROIC is reduced by increasing load capacitor under tradeoff and a low input offset voltage in the range of ±5 mV is obtained by optimizing transistors in the input-stage amplifier. T800 ROIC has been fabricated with 0.5-μm 5V mixed signal CMOS process and interfaced with InGaAs detector arrays. Test results show that ROIC noise is around 90 μV and input offset voltage shows a good correspondence with simulation results. 800×2 InGaAs FPA has a peak detectivity (D*) of about 1.1×1012 cmHz1/2/ W, with dynamic range of above 80dB.

256×1 element linear InGaAs short wavelength near-infrared detector arrays

256×1 element linear InGaAs detector arrays assembly have been fabricated for the short wave infrared band(0.9~1.7μm), including the detector, CMOS readout circuits, thermoelectric cooler in a sealed package. The InGaAs detectors were achieved by mesa structure on the p-InP/i-InGaAs/n-InP double hetero-structure epitaxial material. 256×1 element linear InGaAs detectors were wire-bonded to 128×1 element odd and even ROIC, which were packaged in a dual-in-line package by parallel sealing. The characteristics of detectors and detector arrays module were investigated at the room temperature. The detector shows response peak at 1.62μm with 50% cutoff wavelength of 1.73μm and average R0A with 5.02KΩ•cm2. Response non-uniformity and average peak detectivity of 256×1 element linear InGaAs detector arrays are 3.10% and 1.38×1012cmHz1/2/W, respectively.

Behaviors of beryllium compensation doping in InGaAsP grown by gas source molecular beam epitaxy

We report structural properties as well as electrical and optical behaviors of beryllium (Be)-doped InGaAsP lattice-matched to InP grown by gas source molecular beam epitaxy. P type layers present a high degree of compensation on the order of 1018 cm−3, and for Be densities below 9.5×1017 cm−3, they are found to be n type. Enhanced incorporation of oxygen during Be doping is observed by secondary ion mass spectroscopy. Be in forms of interstitial donors or donor-like Be-O complexes for cell temperatures below 800°C is proposed to account for such anomalous compensation behaviors. A constant photoluminescence energy of 0.98 eV without any Moss-Burstein shift for Be doping levels up to 1018 cm−3 along with increased emission intensity due to passivation effect of Be is also observed. An increasing number of minority carriers tend to relax via Be defect state-related Shockley-Read-Hall recombination with the increase of Be doping density.

Electron-initiated low noise 1064 nm InGaAsP/InAlAs avalanche photodetectors

We report an electron-initiated 1064 nm InGaAsP avalanche photodetectors (APDs) with an InAlAs multiplier. By utilizing a tailored digital alloy superlattice grading structure, a charge layer and a p type InAlAs multiplier, an unity gain quantum efficiency of 48%, a low room temperature dark current of 470 pA at 90% breakdown voltage, and a low multiplication noise with an effective k ratio of ∼0.2 are achieved. The measured maximum gain factor is 5 at room temperature, which is currently limited by the non-optimized electric field profiles, and can be readily enhanced by modifying the doping and thickness parameters for the multiplier and the charge layer.

A 1024×512 ROIC with 30μm pixel pitch and 250Hz high frame rate for shortwave infrared detector

In order to satisfy the requirements of short-wave infrared hyperspectral detection, we developed a 1024 x 512 ROIC with 30μm pixel pitch. CTIA with cascode amplifier was utilized as input stage and CDS was used for eliminating KTC noise and 1/f noise in CTIA. For this large chip with sizes up to 30mm x 20mm, it has been found that column circuit was a major bottleneck to achieve high frame frequency. A solution to solve this problem in this work is to pre-establish the signal of the column amplifier and then buffer odd and even column signals to the bus alternatively. In addition, parasitic capacitance of column-level bus was carefully lowered in layout design. The total readout rate reached 120 Mpixels/s with eight parallel output channels which allowed for a frame rate of 250 Hz.

2.25-

A separated absorption and multiplication avalanche photodiode for light detection to wavelengths as long as 2.25~μm is reported. Photons were absorbed in a metamorphic In_0.75Ga_0.25As layer, while the photo-generated electrons were injected into a lattice-matched In_0.52Al_0.48As multiplier on InP. A responsivity gain of 2.7 was attained at 2 μm at 250 K and increased to 20 at 77 K. A primary dark current of 2.2 × 10^-3 A/cm² at -15 V was measured at 77 K, which is dominated by dislocation defect-assisted tunneling with activation energies between 0.1 and 0.2 eV. This letter demonstrates the potentiality of extending spectral range of avalanche photodiodes in metamorphic device architecture.