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Although Mn2+-doped aqueous ZnSe nanocrystals (NCs) have been reported, the obtained doped NCs usually possess multiple emission peaks originated from nanocrystal bandgap, defects, and Mn-dopants. ...

Based on collection effect of photogenerated carrier, the front-illuminated planar type InGaAs short-wave infrared (SWIR) detectors were fabricated by using N-InP/i-In0.53Ga0.47As/N-InP double-hetero structure materials. The series of detectors with the same dimension of 200μm×200μm contain several lateral collection regions and the width of each collection region is 15μm. The photoelectric characteristics of the photoresponse, I-V, spectral response and detectability of detectors with the lateral collection structure and normal structure were further analyzed. The build-in electrical field could effectively collect the electron/hole pairs generated in the lateral collection regions, so the photoresponse of lateral collection detector at 296 K is quite uniform by the laser beam induced current (LBIC) technology. Furthermore, the average peak detectivity and the density of dark current of the detectors with lateral collection structure reached 2.90× 1012 cm·Hz1/2/W and 3.94 nA/cm2 at -0.1 V respectively. It turns out that the lateral collection structure could effectively improve the dark current properties compared with the normal structure.

Nanocomposites of zinc oxide (ZnO) nanocrystals and liquid crystal N-(4-methoxybenzylidene)-4 -ethoxybenzenamine (MB2BA) were prepared by ultrasonic dispersing technology. The MB2BA/ZnO nanocomposi...

In this work, we fabricated dual-band 800 &times, 2 short-wave infrared (SWIR) indium gallium arsenide (InGaAs) focal-plane arrays (FPAs) using N-InP/i-In0.53Ga0.47As/N-InP double-heterostructure materials, which are often applied in ocean-color remote sensing. Using narrow-band interference-filter integration, our detector-adopted planner structure produced two detection channels with center wavelengths of 1.24 and 1.64 &mu, m, and a full-width half-maximum (FWHM) of 0.02 &mu, m for both channels. The photoelectric characteristics of the spectral response, modulation transfer function (MTF), and detectability of the detector were further analyzed. Our FPAs showed good MTF uniformity with pixel operability as high as 100% for each 800 &times, 1 linear array. Peak detectivity reached 4.39 &times, 1012 and 5.82 &times, 1012 cm&middot, Hz1/2/W at 278 K, respectively, and response nonuniformity was ideal at 2.48% and 2.61%, respectively. As a final step, dual-band infrared detection imaging was successfully carried out in push-broom mode.

VO2(B), VO2(M), and V2O5 are the most famous compounds in the vanadium oxide family. Here, their gas-sensing properties were investigated and compared. VO2(B) nanoflakes were first self-assembled via a hydrothermal method, and then VO2(M) and V2O5 nanoflakes were obtained after a heat-phase transformation in nitrogen and air, respectively. Their microstructures were evaluated using X-ray diffraction and scanning and transmission electron microscopies, respectively. Gas sensing measurements indicated that VO2(M) nanoflakes were gas-insensitive, while both VO2(B) and V2O5 nanoflakes were highly selective to ammonia at room temperature. As ammonia sensors, both VO2(B) and V2O5 nanoflakes showed abnormal p-type sensing characteristics, although vanadium oxides are generally considered as n-type semiconductors. Moreover, V2O5 nanoflakes exhibited superior ammonia sensing performance compared to VO2(B) nanoflakes, with one order of magnitude higher sensitivity, a shorter response time of 14&ndash, 22 s, and a shorter recovery time of 14&ndash, 20 s. These characteristics showed the excellent potential of V2O5 nanostructures as ammonia sensors.

GaN-based light emitting diodes (LEDs) have been grown by metalorganic chemical vapor deposition on Si(111) substrate with and without 3C-SiC intermediate layer (IL). Structural property has been characterized by means of atomic force microscope, X-ray diffraction, and transmission electron microscope measurements. It has been revealed that a significant improvement in crystalline quality of GaN and superlattice epitaxial layers can be achieved by using 3C-SiC as IL. Regarding of electrical and optical characteristics, it is clearly observed that the LEDs with its IL have a smaller leakage current and higher light output power comparing with the LEDs without IL. The better performance of LEDs using 3C-SiC IL can be contributed to both of the improvements in epitaxial layers quality and light extraction efficiency. As a consequence, in terms of optical property, a double enhancement of the light output power and external quantum efficiency has been realized.

This article presents the fabrication of the front-illuminated planar type InGaAs infrared detector based on the lateral collection structure. The detector with the cutoff wavelength 1.7μm was fabricated on the NIN-type InP/InGaAs/InP hetero-structure materials with sealed-ampoule method using Zn3P4 as the diffusion source. And the detector with the dimension of 460μm×1000μm consists of four lateral collection regions and the width of each region is 15μm. Furthermore, the electrical properties and photo response characteristics were investigated between detectors with the lateral collection structure and normal structure. The Laser beam induced current (LBIC) map shows that the photoresponse of lateral collection InGaAs detector at 296 K is quite uniform and the photoresponse signals generated in the lateral collection regions are the same as them in PN junction regions. The lateral collection regions disappear from view since the electron/hole pairs generated in the regions are all collected by the electrical field of depletion region. It turns out that the average peak detectivity and the density of dark current of the detectors with lateral collection structure and normal structure is 3.22×1012 cm·Hz1/2/W and 3.00×1012 cm·Hz1/2/W, 4.85 nA/cm2 and 22 nA/cm2 at -100 mV respectively. Therefore, the lateral collection structure could substantially reduce the dark current by 70% compared with the normal structure.

In order to study the effect of different passivation films on the detector performance, the front-illuminated planar-type 256×1 element InGaAs/InP detectors were fabricated with SiNx film and SiO2 film. The SiNx film was deposited by plasma enhanced chemical vapor deposition (PECVD) and SiO2 film was deposited by magnetron sputtering technology. The electrical properties and photoresponse characteristics were investigated after the detector mounted on dewar. The photoresponse maps from laser beam induced current (LBIC) method show that the isolation of adjacent elements of the detector with SiNx film is better than the detector with SiO2 film. Furthermore, at room temperature the average density of dark current and the average peak detectivity of the two kinds of detector is 26.8 nA/cm2 and 41.2 nA/cm2 at 100 mV reverse bias, 1.21×1012 cm·Hz1/2/W and 1.08×1012 cm·Hz1/2/W respectively. Therefore, the detector with SiNx film deposited by PECVD could availably passivate the surface in comparison with the detector with SiO2 film by magnetron sputtering technology.

The surface passivation of low-temperature-deposited SiNx films has been investigated in PIN type In0.83Ga0.17As photodiodes. In contrast to SiNx films (330 °C) fabricated by PECVD (Plasma enhanced chemical vapor deposition), the low-temperature-deposited SiNx films (75 °C) fabricated by ICPCVD (Inductively coupled plasma chemical vapor depositon) have a good effect on passivation of In0.83Ga0.17As photodiodes, which caused reductions of dark current as large as 2–3 orders of magnitude at the same test temperature 200 K. The effects of low-temperature-deposited SiNx passivations with lowrate (∼16 nm/min) model were compared to the ones with highrate (∼100 nm/min) model. SiNx films with lowrate model have a better effect on reducing dark current of the photodiodes. The different SiNx films were studied by SIMS. The results show that the content of oxides in SiNx layer fabricated by PECVD is 2 orders of magnitude more than that in SiNx layer fabricated by ICPCVD which could be the reason that low-temperature-deposited SiNx passivation leads to higher performance. Further, the dark current density of the photodiodes with lowrate-deposited SiNx passivations does not show the dependence on the perimeter-to-area(P/A) of the junction.

The optical properties of the type-II lineup In x Al1−x N–Al0.59Ga0.41N/Al0.74Ga0.26N quantum well (QW) structures with different In contents are investigated by using the six-by-six K–P method. The type-II lineup structures exhibit the larger product of Fermi–Dirac distribution functions of electron f c n and hole ( 1 − f v U m ) and the approximately equal transverse electric (TE) polarization optical matrix elements ( | M x | 2 ) for the c1–v1 transition. As a result, the peak intensity in the TE polarization spontaneous emission spectrum is improved by 47.45%–53.84% as compared to that of the conventional AlGaN QW structure. In addition, the type-II QW structure with x ∼ 0.17 has the largest TE mode peak intensity in the investigated In-content range of 0.13–0.23. It can be attributed to the combined effect of | M x | 2 and f c n ( 1 − f v U m ) for the c1–v1, c1–v2, and c1–v3 transitions.

Temperature dependence of the optical properties of InGaN/GaN single quantum well light-emitting diodes (LEDs) with different indium (In) contents is investigated by using the effective mass theory taking into account the band-gap shrinkage and lattice thermal expansion. The peak intensity of the spontaneous emission spectrum is decreased by 30.6%, 30.4%, and 30.3% for the violet, blue, and green LEDs in the temperature range 300 K?400?K, while the reductions of internal quantum efficiency (?) with temperature are ~0.13, ~0.11, and ~0.1 respectively at the injection current density of 100 A cm?2. Moreover, two different slopes for all the ??T curves are observed: a lower absolute value of the slopes at T??=??300?350?K; a larger absolute value of the slopes at T??=??350?400?K. The numerical results also indicate that the efficiency droop effect with increasing the temperature becomes more serious, especially for the InGaN/GaN LED structures with the lower In-content.

The effects of temperature on the optical properties of InGaN/GaN quantum well (QW) light-emitting diodes have been investigated by using the six-by-six K-P method taking into account the temperature dependence of band gaps, lattice constants, and elastic constants. The numerical results indicate that the increase of temperature leads to the decrease of the spontaneous emission rate at the same injection current density due to the redistribution of carrier density and the increase of the non-radiative recombination rate. The product of Fermi-Dirac distribution functions of electron f c n and hole ( 1 − f v U m ) for the transitions between the three lowest conduction subbands (c1–c3) and the top six valence subbands (v1–v6) is larger at the lower temperature, which indicates that there are more electron-hole pairs distributed on the energy levels. It should be noted that the optical matrix elements of the inter-band transitions slightly increase at the higher temperature. In addition, the internal quantum...

The stochastic production frontier approach is used to study the effects of education on agricultural efficiency for a cross-section of 'early-stage' farms from Guanghan County, Sichuan Province, China. Education for farm families in rural China is multifaceted with a combination of formal education, intragenerational transfer of knowledge within the home, and agricultural extension services. Since our survey data span two different years with markedly different policy environments, we are able to examine not only which aspects of education affect agricultural efficiency, but also whether or not the policy environment matters. We find limited evidence that in a policy environment that is conducive to agriculture, formal education provides positive returns in agriculture. Furthermore, general education may provide greater returns than the more targeted extension services.

Urbanisation rates in China have been low compared to other countries at similar stages of development. We examine recent trends in China's urbanisation process in the context of a disequilibrium supply and demand model for urban residents with relative urban food consumption as a proxy for wages. This model takes into consideration the roles of the agricultural and industrial sectors in the context of a non-market economy where institutional arrangements and policy regimes play important roles in determining urbanisation levels. We find persistent periods of disequilibrium prior to the introduction of reforms in 1978. Throughout the post-reform era there has been a markedly improved balance between urban population levels, urban food consumption, and industrial and agricultural production levels.

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.

In x Ga 1-x As ternary compound is suitable for detector applications in the shortwave infrared (1-3 μm) band. The alloy In 0.53 Ga 0.47 As is lattice-matched to InP substrate, which leads to high quality epitaxial layers. Consistently the In 0.53 Ga 0.47 As detector shows low dark current density and high detectivity at room temperature with wavelength response between 0.9 and 1.7 μm. In this paper, planar-type 24×1 linear InGaAs detector arrays with guard-ring structure were designed and fabricated based on n-i-n + type InP/In 0.53 Ga 0.47 As/InP epitaxial structure by sealed-ampoule diffusion method. At first the dark current density is about 30~60 nA/cm 2 at -0.1 V at room temperature. After modifications to the detector design and processing, the dark current density reduces to 2~9 nA/cm 2 at -0.1 V at 293 K. The ideality factors simulated from I-V curves come close to 1 and less than the factors of previous detectors, which indicates that the dark current is dominated by diffusion current, while the generation-recombination current exhibits in the previous detectors. At the temperature of 293 K, the R 0 A of the detector reaches more than 1×10 7 Ω·cm 2 , the relative spectral response is in the range of 0.9 μm to 1.68 μm, the mean peak responsivity is 1.2 A/W and the mean peak detectivity is more than 3.0×10 12 cm·Hz 1/2 /W.

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 (ρ c =8.88×10 -4 Ωcm 2 ) 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.

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 L p is about 19.6µm at 296K. The density of dark current is 13.4nA/cm 2 at 100mV reverse bias and the peak detectivity is 3.4×1012cmHz 1/2 W -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.

Scanning capacitance microscopy (SCM) and scanning spreading resistance microscopy (SSRM) both are capable of mapping the 2-demensional carrier distribution in semiconductor device structures, which is essential in determining their electrical and optoelectronic performances. In this work, cross-sectional SCM1,2 is used to study the InGaAs/InP P-i-N junctions prepared by area-selective p-type diffusion. The diffusion lengths in the depth as well as the lateral directions are obtained for junctions under different window sizes in mask, which imply that narrow windows may result in shallow p-n junctions. The analysis is beneficial to design and fabricate focal plane array of near infrared photodetectors with high duty-cycle and quantum efficiency. On the other hand, SSRM provides unparalleled spatial resolution (

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 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.