Xiaoli Wu

Effects of an anodic oxide passivation layer on mesa-type InGaAs (PIN) photodetectors

Because of the high density of surface states and large surface recombination velocity found in III–V materials, surface passivation remains a crucial processing step for the fabrication of mesa-type InGaAs photodetectors. It is required to find an easy and economical method to form an effective passivation layer on the surface of the detector. In this work, an oxide passivation layer formed by electrochemical anodization was proposed and a 256-element In0.78Ga0.22As photodetector array was fabricated. The dark current performance achieved is as low as 2 × 10−7 A (bias voltage of −0.1 V) at 300 K. The reduction of dark current indicates that the anodic oxide passivation layer is effective in reducing recombination at the exposed mesa surface.

Effect of sulfur passivation on the InP surface prior to plasma-enhanced chemical vapor deposition of SiNx

The fabrication of Au/SiNx/InP metal–insulator–semiconductor (MIS) diodes has been achieved by depositing a layer of SiNx on the (NH4)2Sx-treated n-InP. The SiNx layer was deposited at 200 °C using plasma-enhanced chemical vapor deposition (PECVD). The effect of passivation on the InP surface before and after annealing was evaluated by current–voltage (I–V) and capacitance–voltage (C–V) measurements, and Auger electron spectroscopy (AES) analysis was used to investigate the depth profiles of several atoms. The results indicate that the SiNx passivation layer exhibits good insulative characteristics. The annealing process causes distinct inter-diffusion in the SiNx/InP interface and contributes to the decrease of the fixed charge density and minimum interface state density, which are 1.96 × 1012 cm−2 and 7.41 × 1011 cm−2 eV−1, respectively. A 256 × 1 InP/InGaAs/InP heterojunction photodiode, fabricated with sulfidation and SiNx passivation layer, has good response uniformity.

Improved Au/Zn/Au ohmic contacts for p-type InP

In this work, an innovated Si3N4 as an out-diffusion barrier layer to Au/Zn/Au contact system for p-type InP has been proposed. Before the contacts were annealed, Si3N4 layer was deposited on the Au(200Å)/Zn(700Å)/Au(200Å), then the Si3N4 was removed by HF and a 2000A layer of pure gold was deposited to facilitate wire bonding. The specific contact resistance dropped to a minimum value of 6×10-7 Ω • cm2 (for an acceptor concentration of about 3×1018 cm-3) and the contact became perfectly Ohmic. Besides, Si3N4 layer is an excellent passivation layer and antireflection coating in InP/InGaAs/InP (p-i-n) photodiodes.

Properties of Au/Pt/Ti contact to p-InP by rapid thermal processing

We found that the contact resistance of Au/Pt/Ti on p-InP increases with the increase of annealing time and annealing temperature. Au/Pt/Ti is ohmic contact metal as deposited with specific contact resistance of 2.49×10-3 Ωcm2 when p-InP doped by 7.5×1018 cm-3 and is Schottky contact when doped by 2×1018 cm-3. Surface morphologies of Au/Pt/Ti after rapid thermal processing (RTP) were analyzed by atom force microscopy (AFM). An interface layer dominated by TiIn compound, which increase the specific contact resistance, was found in Auger electron spectroscopy (AES) analysis. P-InP and n-InP ohmic contacts can be achieved at the same time as deposited when added p-In0.53Ga0.47As layer on p-InP/InGaAs/n-InP without annealing.

Recombination lifetime characterization and mapping of p-i-n InP/Ln 0.53 Ga 0.47 As/InP mesa structure using the microwave photoconductivity decay (μ-PCD) technique

The uncooled InGaAs-based infrared detector has received great interest in recent years for its application in optical-fiber communication and remote sensing. However, the improvement of device performance is hampered by the lack of feasible method to monitor its device process. The Microwave Photoconductivity Decay (μ-PCD) technique is a contactless and non-destructive technique of the recombination lifetime characterization and mapping and has found wide application in semiconductor research. In this paper, a double heterojunction p-i-n InP/In0.53Ga0.47As/InP mesa structure was fabricated by Ar+ ion etching and the μ-PCD technique was applied to characterize the electrical effects of ion etching on this structure. The results revealed that the built-in field in the p-n junction played a critical role in recombination of photo induced minority carriers which made the mesa structure identifiable but not identical with the lifetime mapping of the sample. The recombination lifetime in the mesa was dominated by the recombination process in the edge of the mesa. The lifetime in the etched region was also influenced by the built-in field and increased with the decrease of distance to the mesa area. And ion etching brought great nonuniformity to the photo active cells.

Performance analysis of 256 element linear 2.4μm InGaAs photovoltaic detector arrays

In this work, the performance of InxGa1-xAs photovoltaic detectors with cutoff wavelength of 2.4μm(x=0.78) were investigated. The detector arrays were fabricated using gas source molecular beam epitaxy (GSMBE) grown material and arranged in linear arrays of 256 pixels of 56×56μm2 dimension. The transition of the large lattice mismatch (1.6%) between the substrate and the absorption layer was dealt with a linearity transformation InxGa1-xAs buffer layer. The dark-current performance achieved is as low as 10-10A at 300K and a bias voltage of -0.5V. This corresponds to a figure of merit for detector resistance R0 times detector pixel area A of R0A =3.5~7.5Ωcm2 at 300K and quantum efficiency above 60%. Room temperature D*(λp) values beyond 3×1010cmHz1/2W-1.

256×1 doped-InGaAs mesa infrared focal plane array

We have made 256x1 front-illuminated mesa doped-InGaAs infrared focal plane array (FPA) with two CTIA-structure L128 read out integrate circuit at two sides. The mean peak detectivity of the detectors is 1.33x10¹² cmHz^1/2W^-1 at 278 K. The un uniformity of response is 19.3% at room temperature.