Zuyao Zhou

A voltage-controlled tunable two-color infrared photodetector using GaAs/AlAs/GaAlAs and GaAs/GaAlAs stacked multiquantum wells

A voltage‐controlled tunable two‐color infrared detector with photovoltaic (PV) and photoconductive (PC) dual‐mode operation at 3–5 μm and 8–14 μm using GaAs/AlAs/AlGaAs double barrier quantum wells (DBQWs) and bound‐to‐continuum GaAs/AlGaAs quantum wells is demonstrated. The photoresponse peak of the photovoltaic GaAs/AlAs/GaAlAs DBQWs is at 5.3 μm, and that of the photoconductive GaAs/GaAlAs quantum wells is at 9.0 μm. When the two‐color detector is under a zero bias, the spectral response at 5.3 μm is close to saturate and the peak detectivity at 80 K can reach 1.0×1011 cmHz1/2/W, while the spectral photoresponsivity at 9.0 μm is absolutely zero completely. When the external voltage of the two‐color detector is changed to 2.0 V, the spectral photoresponsivity at 5.3 μm becomes zero while the spectral photoresponsivity at 9.0 μm increases comparable to that at 5.3 μm under zero bias, and the peak detectivity (9.0 μm) at 80 K can reach 1.5×1010 cmHz1/2/W. Strictly speaking, this is a real bias‐controlled...

INVESTIGATION OF PERIODICITY FLUCTUATIONS IN STRAINED (GANAS)1(GAAS)M SUPERLATTICES BY THE KINEMATICAL SIMULATION OF X-RAY DIFFRACTION

Periodicity fluctuations of layer thickness and composition in a superlattice not only decrease the intensity, they also broaden the width of the satellite peaks in the x-ray diffraction pattern. In this letter, we develop a method that is dependent on the width of satellite peaks to assess periodicity fluctuations of a superlattice quickly. A linear relation of the magnitude of fluctuations, peak width and peak order has been derived from x-ray diffraction kinematical theory. By means of this method, periodicity fluctuations in strained (GaNAs)(1)(GaAs)(m) superlattices grown on GaAs substrates by molecular beam epitaxy have been studied. Distinct satellite peaks indicate that the superlattices are of high quality. The N composition of 0.25 and its fluctuation of 20% in a strained GaNxAs1-x monolayer are obtained from simulations of the measured diffraction pattern. The x-ray simulations and in situ observation results of reflection high-energy electron diffraction are in good agreement

Comparison of Cu gettering to H+ and He+ implantation-induced cavities in separation-by-implantation-of-oxygen wafers

Well-defined bands of cavities have been formed beneath the buried oxide (BOX) layer of two sets of separation-by-implantation-of-oxygen (SIMOX) wafers by H+ and He+ implantation. The gettering of Cu impurities, which were implanted into the top Si layer at different doses (5×1013, 5×1014, and 5×1015/cm2), to the cavities has been studied by secondary ion mass spectroscopy and cross-sectional transmission electron microscopy. The results indicated that the cavities induced either by H+ or He+ implantation are effective gettering centers for Cu in SIMOX wafers, and up to 4×1015/cm2 Cu has diffused through the BOX layer and been captured by the cavities. The gettering efficiency of cavities increases with the decrease of Cu implantation doses and the increase of annealing temperatures. He+ ion implantation is found to be more suitable for cavity formation and impurity gettering than H+ ion implantation.

HIGH ACTIVATION EFFICIENCY IN MG+ IMPLANTED GAAS BY P+ COIMPLANTATION

Coimplantation of 125 keV Mg+ ions and 160 keV P+ ions with the same dose of 5×1014 cm−2 was investigated. Samples were annealed in a conventional furnace or a halogen tungsten lamp rapid thermal annealing system. It was found that the additional implant of P+ improves the electrical quality of the Mg+ implanted GaAs more effectively than additional implant of As+. By using rapid thermal annealing, a maximum activation efficiency of 92% with a sheet resistance of 145 Ω/⧠ was obtained for Mg+ and P+ coimplantation after an anneal at 1050 °C for 5 s, while the maximum activation efficiency for Mg+ single implant was 36% corresponding to a sheet resistance of 358 Ω/⧠ after an anneal at 800 °C for 5 s. Coimplantation of P+ evidently can also reduce the redistribution of the implanted Mg.

Observation of slow positron annihilation in silicide films formed by solid state interaction of Co/Ti/Si and Co/Si

Slow positron beam was used to investigate the solid state reaction of Co/Si and Co/Ti/Si. Variable‐energy (0–20 keV) positrons were implanted into samples at different depths. The Doppler broadening of the annihilation γ‐ray energy spectra measured at a number of different incident positron energies were characterized by a line‐shape parameter ‘‘S.’’ It was found that the measured S parameters were sensitive to thin‐film reaction and crystalline characteristics. In particular, the S parameter of epitaxial CoSi2 formed by the ternary reaction was quite different with that of the polycrystalline CoSi2 formed by direct reaction of Co with Si.

Nanocavities: an Effective Gettering Method for Silicon-on-Insulator Wafers

The 4×1016 / cm2 H+ and 9 × 1016 / cm2 He+ have been implanted into the silicon substrate of separation-by-implantation-of oxygen (SIMOX) wafers, respectively, followed by a 700°C annealing to form nanocavities beneath the buried oxide (BOX) layer. The SIMOX wafers were intentionally contaminated with Cu impurities by implanting different doses of Cu in the top Si layer. Secondary ion mass spectroscopy and cross-sectional transmission electron microscopy technologies have been employed to investigate the gettering effect of nanocavities to the Cu impurities. The cavities induced either by H+ or He+ implantation are effective gettering centers for Cu in SIMOX wafers. After annealing at 1000°C for 90 min, up to 4×1015 / cm2 Cu has diffused through the BOX layer and been captured by the cavities. The gettering efficiency of cavities increases with the decrease of Cu implantation doses. The nanocavities provide an attractive method for gettering transition metal impurities in SIMOX materials.

Experimental studies of N+ implantation into CVD diamond thin films

The effects of N+ implantation under various conditions on CVD diamond films were analyzed with Raman spectroscopy, four-point probe method, X-ray diffraction (XRD), Rutherford backscattering spectroscopy (RBS), ultraviolet photoluminescence spectroscopy (UV-PL), Fourier transformation infrared absorption spec|troscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The results show that the N+ implantation doping without any graphitization has been successfully realized when 100 keV N+ ions at a dosage of 2×1016 cm−2 were implanted into diamond films at 550°C. UV-PL spectra indicate that the implanted N+ ions formed an electrically inactive deep-level impurity in diamond films. So the sheet resistance of the sample after N+ implantation changed little. Carbon nitride containing C≡N covalent bond has been successfully synthesized by 100 keV, 1.2×1018 N/cm2 N+ implantation into diamond films. Most of the implanted N+ ions formed C≡N covalent bonds with C atoms. The others were free state nitrogen, which existed in the excessive nitrogen layers. C(1s) XPS studies show the existence of three different C(1s) bonding states, corresponding to graphite, i-carbon and the carbon of C≡N covalent bonding state, respectively, which agrees well with the Raman results.

Growth of epitaxial CoSi2 on SIMOX material by a solid-phase reaction of deposited TiN/Co/Ti layers

Abstract Co/Ti bimetallic layers and a TiN capping layer were sequentially deposited on a SIMOX wafer. The influence of the residual oxide on the Si surface was reduced by depositing Ti first. Subsequently an epitaxial CoSi 2 film was grown by the interaction of the Co with the Si overlayer of the SIMOX through a multistep anneal in a nitrogen ambient. Both Rutherford backscattering analysis and cross-sectional transmission electron microscopy have shown that a good quality epitaxial growth of CoSi 2 with an abrupt interface has been achieved. The interface contained only a few coherent steps which were generated to relax the mismatch strain of the CoSi 2 with the Si layer. A minimum channeling yield of 30% was achieved for the epitaxial CoSi 2 film. Although the value is higher than that of CoSi 2 formed on bulk single-crystalline Si, it is comparatively low for epitaxial CoSi 2 growth on the Si(100) overlayer of SIMOX when formed by a solid-phase reaction.

Electrical and Optical Properties of Si + and P + Implanted InP:Fe

Dual implantations of Si + and P + into InP:Fe were performed both at 200°C and room temperature. Si + ions were implanted by 150keV with doses ranging from 5×10 13 /cm 2 to 1×10 15 /cm 2 , while P + ions were implanted by 110keV. 160keV and 180keV with doses ranging from 1×l0 13 /cm 2 to 1×10 15 /cm 2 . Hall measurements and photoluminescence spectra were used to characterize the silicon nitride encapsulated annealed samples. It was found that enhanced activation can be obtained by Si + and P + dual implantations. The optimal condition for dual implantations is that the atomic distribution of implanted P overlaps that of implanted si with the same implant dose. For a dose of 5×l0 14 /cm 2 , the highest activation for dual implants is 70% while the activation for single implant is 40% after annealing at 750°C for 15 minutes. PL spectrum measurement was carried out at temperatures from 11K to 100K. A broad band at about 1.26eV was found in Si + implanted samples, of which the intensity increased with increasing of the Si dose and decreased with increasing of the co-implant P + dose. The temperature dependence of the broad band showed that it is a complex (V p -Si p ) related band. All these results indicate that silicon is an amphoteric species in InP.