Yaoming Zhu

Analysis of pn-junction degeneration in heating process for extended wavelength InGaAs detectors

To improve the operability and rate of final products significantly, a novel process was proposed. Detectors with cutoff wavelength at 1.7 μm and 2.4 μm were fabricated in different processes, and the electricity characteristics and spectral response were measured. The novel process was analyzed by comparing the characteristics of the detectors. The dark current and responsibility of the detectors with cutoff wavelength at 1.7 μm fabricated in the new process were improved. However, the new process has negative effect on the detectors with cutoff wavelength at 2.4 μm. The pnjunction degenerated and the leakage current increased sharply. In order to find the reasons of degeneration, the methods of Auger electron spectroscopy (AES) and scanning capacitance microscope (SCM) were used. The results indicate that the metal elements do not penetrate into the pn junction causing the sharp increase of leakage current, while the interface states due to lattice mismatch are thermally activated causing the degeneration of pn- junction.

The influence of sunlight irradiation on the characteristics of InGaAs detectors

InGaAs ternary compound is suitable for detector applications in the shortwave infrared (SWIR) band. Due to the advantages of good stability, low cooling requirements and high detectivity, InGaAs detectors have been applied widely in the space remote sensing area. However, InGaAs detectors would be affected by strong sunlight direct irradiation in space application. In this paper, a mesa-type InGaAs detector with large sensitive area of diameter 5mm was designed based on InP/In0.53Ga0.47As/InP epitaxial material, which is lattice-matched to InP substrate. The InGaAs detectors were fabricated by ICP etching, and packaged in a Kovar shell. The relative spectral response is in the range of 0.9μm to 1.7μm. The mechanism of the sunlight direct irradiation on InGaAs detector performance was studied. The sunlight were focalized by lens and irradiated directly on the detector. A piece of epitaxial material was investigated at the same time which was cleaved from a 2 inch wafer, same to the detector material. The real time testing was taken out to observe the output signal of the detector. After the irradiation experiment, the I-V curves and the relative response were tested immediately. The dark current of the detector increased temporarily, but come back to the original level after 24 hours. The response spectrum was nearly not affected. The XRD testing of the epitaxial material sample was carried out before and after sunlight direct irradiation. The sunlight irradiation causes thermal stress degradation. The thermal electrons were produced by the absorption of a great deal of visible light, leading to local enhancement of temperature and the lattice degeneration of the material.

The temperature-dependent photoresponse uniformity of an InGaAs subpixels infrared detector by the LBIC technique

The front-illuminated InP/InGaAs/InP PIN hetero-junction photovoltaic subpixels infrared detector has been achieved based on the lateral collection effect of photogenerated carriers. The photoresponse uniformity of the detector is carried out with a LBIC technique at different temperatures between 88 K and 296 K. With the aid of LBIC and the scanning capacitance microscopy (SCM) technique, the holes diffusion length Lp related to temperature was obtained. The result shows that the photoresponse uniformity decreases with temperature dropping, and Lp also varies directly in proportional to . The acoustic phonon scattering is the chief scattering mechanism existing in the detector with doped InGaAs (n ≈ 5×1016 cm−3) in the measured temperature range. The LBIC technique can be utilized effectively in the measurement of photoresponse uniformity of InGaAs infrared detectors, especially for the InGaAs subpixels detectors.

Research on ICP etching technology of InGaAs based on orthogonal experimental design

A chemistry of halogen mixed with neural or inert gas is mostly used for ICP etching of III-V compound semiconductor. The neural or inert gas has an effect of desorption and dilution, on the other hand, damages in the lattice due to ion bombardment are induced, which result in difficulties in improving the performances of detectors. Good desorption and passivation was obtained by using a new etching technology with the mixed gas of methane and hydrogen instead of neural or inert gas, and the damages caused by physical bombardment were much less because of the small quality of radical. The sample etched by using this technology was compared with the ones by using etching of neural or inert gas. The influences of ICP etching process parameters on etch rate, surface roughness and surface damage were investigated by using orthogonal experimental design. The methods of scanning electron microscopy (SEM) and X-ray Diffraction (XRD) were used to investigate the surface profile and surface damage respectively. And according to the experimental results, the process parameters are optimized. Finally, a feasible etching technology with low damage, good surface profile and good controllability was achieved.

Analysis of cross talk in high density mesa linear InGaAs detector arrays using tiny light dot

With the development of material growth and device technologies, the pixel density becomes much higher. The pixel size and the spacing between pixels have been becoming smaller and smaller, causing the cross talk of the neighboring pixels acuter. Linear InGaAs detector arrays with 25 μm pitch and 2 μm spacing were fabricated, and the modulation transfer function of detector arrays with infrared lens was measured using a system of collimator tube. A tiny light dot produced by the collimator tube was used to analyze and calculated the cross talk of the detector with conserved absorber around the photosensitive mesa, and the cross talk between two neighboring pixels was approximately estimated. With the conserved absorber structure, the electronic cross talk is dominant in the cross talks between neighboring pixels.

Front-illuminated planar type InGaAs sub-pixels infrared detector

This article presents the fabrication of the front-illuminated planar type InGaAs sub-pixels infrared detector with the cutoff wavelength 1.68µm based on the lateral collection effect of photogenerated carriers. The detector with the dimension of 385µm×500µm consists of five sub-pixels and each of which has two sub-elements. The electrical properties and photo response characteristics were investigated after the detector mounted on Dewar. The photoresponse map from Laser beam induced current (LBIC) method shows that the detector has good photoresponse uniformity at 296K which indicates the electron/hole pairs generated in the lateral collection regions are all collected by the nearest sub-elements. The minority carrier diffusion length Lp is about 19.6µm at 296K. The density of dark current is 13.4nA/cm2 at 100mV reverse bias and the peak detectivity is 3.4×1012cmHz1/2W-1 at room temperature. By reducing the diffusion region, the detector could effectively decrease the lattice damage and corrosion spots in the cap layer caused in the PN junction formation without sacrificing detector performance. Therefore, this structure could availably reduce the ratio of dead pixels, suppress the extension of photo-sensitive area and the optical cross-talk in photo detector arrays.

Contact property of Ni(Ti)/Pt/Au on p-In0.52Al0.48As

The annealing effects of rapid thermal processing in N2 from 350 °C to 500 °C for 60 s on Ni/Pt/Au contacts to p-InAlAs have been investigated. The result indicated that the contacts were all Schottky contacts and lowest barrier height(0.67eV) was achieved at about 450 °C. Then we used evacuated sealed-ampoule Zn diffusion method to form a heavily doped layer on p-InAlAs layer of the same sample. The diffusion conditions were 530 °C &4 min and 530 °C &8 min, respectively. Also Ni/Pt/Au contacts were deposited on the two samples and annealed at 450 °C &60 s. Although I-V characteristics which were measured indicated that a heavily doped layer is beneficial for the cantacts properties, the contacts were still Schottky contacts and the barrier heights were reduced to 0.54 eV and 0.57 eV for the two samples. Finally, we investigated contacts property of Ti/Pt/Au on p-In0.52Al0.48As of the sample which is Zn-diffused at 530 °C for 4 min. The sample was annealed at 450 °C for 60 s and the contact resistivity of the contacts was determined using the transfer line model measurements. Low resistance ohmic contacts (ρc=8.88×10-4 Ωcm2) were achieved. The results indicated that the contacts property is controlled by chemical and metallurgical reaction between the contact metal and the InAlAs layer, and a heavily doped layer is beneficial to contact properties.