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This paper investigates the manufacturability-aware process of p-n junction formation for photovoltaic cells involving with Si nanoparticle layer. The furnace-based dopant diffusion process of forming a p-n junction consumes a substantial amount of energy. In addition, repetitive production steps prevent the possibility of Si ink-based cells integrating onto flexible substrates. This research examined the local heating dopant diffusion process by using a fiber laser at a wavelength of 1064 nm. The infrared beam is delivered onto the wafer stack with a nanoparticle carbon layer and n-type Si ink layer on p-type Si substrates. The nanoparticle carbon film absorbs infrared beam energy and converts photon energy as a thermal source to diffuse the n-type dopant in Si ink into the p-type Si wafer. The Si ink in this paper contains a mixture of Si nanoparticles and an n-type spin-on dopant solution. The TEM results show that Si nanoparticles are uniformly dispersed on the Si wafer surface. This research investigated sheet resistance as a function of laser parameters, including laser power, scanning speed, and pulse frequency for the samples coated with Si ink. Secondary ion mass spectroscopy measurements indicate the presence of an n-type dopant in p-type substrates, with an approximate diffusion depth of 100 nm. The results indicate that the proposed infrared laser treatment technique is promising for the formation of p-n junctions with Si ink-based photovoltaic cells.

The simulation and experimental measurement of the charge storage characteristics in Ge/Si hetero-nanocrystals based MOS memory structure have been performed. Owing to the Ge/Si hetero-energy bands, comparing with Si nanocrystal memory, the retention time increases remarkably. The trade-off between the speed programming and the long retention could be solved efficiently, and the performance of the device is substantially improved.

In this paper X-ray photoelectron spectrum and Auger electron spectrum were used to study the microstructure of AlGaN/AlN/Si [111] grown by metal organic chemical vapor deposition. The results indicated that a broad transition region, composed of AlN, Si/sub 3/N/sub 4/, SiN/sub x/ (x

Crystal tilts in the lateral overgrowth of GaN over SiO/sub 2/ mask on Sapphire Substrate by HVPE away from the opening region are demonstrated and characterized by scanning electron (SEM) and high resolve x-ray diffraction (HRXRD). The tilts and stripe morphologies are directly related to the mask width and "fill factors" (ratio of stripe opening width to stripe period). It is found that the growth condition, such as the introduction HCl, C/sub 3/H/sub 8//H/sub 2/ and the growth rate also have a significant effect on the wing tilt. The mechanisms of these factors affecting the wing tilts and stripe morphologies are discussed respectively.

Forward and reverse current-voltage characteristics of the Pt Schottky contacts on modulation-doped Al/sub 0.22/Ga/sub 0.78/N/GaN heterostructures were investigated. The barrier height of 0.94 eV and the ideality factor of 1.4 were obtained for the sample with the Si-doping level of 7.5 /spl times/ 10/sup 17/ cm/sup -3/ in the top Al/sub 0.22/G/sub 0.78/N barrier layer. The barrier height is lower and the ideality factor is larger for the samples with higher Si-doping level in the barrier. The reverse current mechanism are also different for the samples with different doping level of the Al/sub 0.22/Ga/sub 0.78/N barrier. It is suggested that the interfacial properties are crucial to the current-voltage characteristics of the samples. Capacitance-frequency measurement indicates that the density of the metal-semiconductor interfacial states are higher for the samples with higher Si-doping level in the barrier. It is thought that the chemical properties of the Al/sub 0.22/Ga/sub 0.78/N surface are influenced by the Si-doping level of Al/sub 0.22/Ga/sub 0.78/N, resulting in the difference in Pt/Al/sub 0.22/Ga/sub 0.73/N interfacial properties.

N-type GaN films grown by Hydride Vapor Phase Epitaxy technique were etched under different conditions at room temperature. Direct evidence of etch-stop effect of dislocations during photoelectrochemical (PEC) etching has been found. Further investigation of the mechanism has been discussed.

Magnetotransport properties of the two-dimensional electron gas (2DEG) in Al/sub x/Ga/sub 1-x/N/GaN heterostructures have been investigated. We extrapolate that the second subband in the triangular quantum well at the heterointerface starts to be populated at a 2DEG concentration of about 7.23 /spl times/ 10/sup 12/ cm/sup -1/. The quantum scattering time related to the first subband is obtained as 0.144-0.146 ps for the heterostructures. Intersubband scattering is also observed in the heterostructures.

Modulation-doped Al/sub 0.22/Ga/sub 0.78/N/GaN heterostructures with different Al/sub 0.22/Ga/sub 0.78/N barrier thickness were grown by means of metal-organic chemical vapor deposition. The Al/sub 0.22/Ga/sub 0.78/N layer is still pseudomorphic growth when its thickness is 53 nm. The mobility of the two dimensional electron gas (2DEG) at the heterointerfaces is much higher than that of the electrons in GaN films at both 300 K and 77 K. The dramatic decrease of the 2DEG mobility in an Al/sub 0.22/Ga/sub 0.78/N/GaN heterostructure corresponds to the partial relaxation of the Al/sub 0.22/Ga/sub 0.78/N barrier.

Gallium Nitride films grown on sapphire substrates were successfully separated by laser radiation. The absorption of the 248 nm radiation by the GaN at the interface results in rapid thermal decomposition of the interfacial layer, yielding metallic Ga and N/sub 2/ gas. The substrate can be easily removed by heating above the Ga melting point of 30/spl deg/C. Atomic force microscopy, X-ray diffraction and Photoluminescence of GaN before and after lift-off process have been performed, which demonstrated that the separation and transfer process do not alter the structural quality of the GaN films. And further discussions on the threshold energy and crack-free strategies of laser lift-off process have also been presented.

The effect of additional HCl on the surface morphology of HVPE GaN was investigated. The introduction of additional HCl to the growth zone altered the polar growth direction at the initial growth stage, and finally the Ga-face polarity GaN films with smooth surface were obtained.

AlGaN/GaN/AlGaN ultraviolet photodetectors were grown on Si [111] substrates using an AlN buffer by metalorganic chemical vapor deposition. These detectors showed a high response in a narrow range of wavelength with a peak position at 365 nm. A peak responsivity of 24 A/W was obtained at 5.5 V bias. This high responsivity is mainly due to the high polarization electric-field in GaN layer of AlGaN/GaN/AlGaN heterojunction structure and the potential wells at AlGaN/GaN interfaces.

The single electron memory effect in TiO/sub x/ nanostructure (thickness 3nm, length 150 nm and width 150 nm) based on localized density of state (LDOS) in metallic oxides is observed. The potential of application in the single electron memory is discussed.

In this work, we have performed epitaxy of Ge dots over Si nanometer-scale columns on Si (100) substrate. A two-step fabrication process has been developed. First, Si buffer layer is deposited on Si substrate by LPCVD and then Ge dots grow on the Si layer. The Ge dots on Si with the packing density as high as 1.6x 10/sup 12/cm/sup -2/ and the average size is 8nm. SEM, XRD, and HRTEM measurements indicate that Ge dots were formed on each nanometer Si column separately. This growth obeys the Stranski-Krastanov (S-K) mode in local area.

In this paper, we firstly present an overview of silicon nanocrystal memories. The performance and fabrication characteristics of the hetero-nanocrystal memories are mainly studied. These devices demonstrate high promising potential as candidates for future deep-submicron embedded memories.

Classical transport and magnetotransport of the two-dimensional electron gas (2DEG) in modulation-doped Al/sub x/Ga/sub 1-x/N/GaN heterostructures have been investigated. In magnetotransport measurements at low temperatures and high magnetic fields, strong Shubnikov-de Hass (SdH) oscillations with double periodicity are clearly observed, indicating the 2DEG occupation of the double subbands in the triangular quantum well at the heterointerfaces. Based on the observation of the SdH oscillation with double periodicity, the sheet concentrations and the mobilities of the 2DEG in the first and the second subbands, magneto-intersubband scattering (MIS) oscillations of the 2DEG, and the spin splitting of the 2DEG in the quantum well at the heterointerfaces are studied and discussed.

Influence of relaxation on the two-dimensional electron-gas (2DEG) in Al/sub x/Ga/sub 1-x/N/GaN/Al/sub y/Ga/sub 1-y/N double heterostructure (DH) is investigated by self-consistently solving the coupled Schrodinger and Poisson equations. The GaN channel layer is in compressive strain on a relaxed AlGaN lower barrier (LB) so as to improve the Al content in the Al/sub x/Ga/sub 1-x/N top barrier (TB) to be double that in the LB (y) and hence the 2DEG density is greatly improved. It is found that the 2DEG sheet density increases with increasing Al content in the TB and achieves a maximum N/sub S/=3.88/spl times/10/sup 13/ cm/sup -2/ at x=0.88 (with y=0.38), even behind the onset of relaxation at x=0.76, indicating the dominant influence of the polarization effect and the quantum confinement effect. Further increasing x reduces N/sub S/ due to significant relaxation. Taking relaxation, R, into account, the 2DEG sheet density increases with increasing Al content in the Al/sub y/Ga/sub 1-y/N lower barrier (LB), opposite to the case of fully strained.

The oxidation of InN and In-rich InN films grown on (0001) sapphires by low-pressure MOCVD has been investigated. X-ray diffraction (XRD) measurements show that stoichiometric InN is difficult to be oxidized at the temperature lower than 400/spl deg/C. However, nonstoichiometric In-rich InN can be oxidized at low temperature even as low as 300/spl deg/C. And In-rich InN films are fully oxidized at 450/spl deg/C. According to the scanning electron microscope (SEM) images, the oxidization of metal In grains on the surface of In-rich InN film is the main process at the temperature lower than 400/spl deg/C. Above 400/spl deg/C, metal In and InN begin to be oxidized simultaneously, which also indicates that stoichiometric InN is difficult to be oxidized at the temperature less than 400/spl deg/C.

The temperature dependence of strain in a 50-nm- and a 100-nm-thick Al/sub 0.2/Ga/sub 0.8/N/GaN heterostructures were investigated at temperatures 300-800 K. The results show that the temperature behavior of the in-plane strain in the 50-nm-thick AlGaN layer is different to that in the 100-nm-thick AlGaN layer. There exists an initial energy barrier to the strain relaxation for the 50-nm-thick Al/sub 0.22/Ga/sub 0.78/N/GaN heterostructure. Meanwhile, for both the 50-nm-and 100-nm-thick AlGaN layers the strain relaxation becomes saturated at the high temperature segment, although the temperature at the point of saturation is different. The total strain relaxation is less than 5% for both the 50-nm- and 100-nm-thick Al/sub 0.22/Ga/sub 0.78/N layers at whole temperature range in our measurements.

Influence of the polarization-induced electric field on the subband structure and the electron distribution in the Al/sub x/Ga/sub 1-x/N/GaN coupled double quantum wells (DQWs) has been studied by solving the coupled Schrodinger's and Poisson 's equations self-consistently. It is found that although the two wells have the same width and the same depth the polarization-induced potential drop leads to the asymmetric potential profile of the Al/sub x/Ga/sub 1-x/N/GaN DQWs, The polarization-induced Stark shift leads to the drastic change of the relative location between the even and the odd order subband levels, and thus resulting in the asymmetric distribution of the electron in the two wells.

Thick GaN films grown with different V/III ratio on sapphire by hydride vapour phase epitaxy have been investigated. The V/III ratio is changed from 240 to 30. All the GaN films, which are n type, show only (0002) oriented peak and have the band emission with no yellow luminescence bands. When V/III ratio is 30, the full width at half maximum of (0002) X-ray rocking curve is the smallest, line-width of the band edge emission is narrow, the surface morphology shows step-flow growth and the growth rate is the highest.

The ohmic contacts of Ti/Al/Ni/Au and Ti/Al/Pt/Au multi-layer on unintentionally-doped Al/sub 0.22/Ga/sub 0.78/N/GaN heterostructures have been investigated. The specific contact resistivities of 1.26/spl times/10/sup -6/ /spl Omega//spl middot/cm/sup 2/ for Ti/Al/Ni/Au contact and 1.97 /spl times/ 10/sup -5/ /spl Omega//spl middot/cm/sup 2/ for Ti/Al/Pt/Au contact were obtained. It is found that the Pt element in Ti/Al/Pt/Au multi-layer influent the diffusion of Al atom into the Au layer, which results in the higher contact resistivity of Ti/Al/Pt/Au contact than that of Ti/Al/Ni/Au one. The formation of excellent ohmic contact on the Al/sub 0.22/Ga/sub 0.78/N/GaN heterostructures is attributed to the existing of a compatible barrier between the metal electrode and the carrier channel at the Al/sub 0.22/Ga/sub 0.78/N/GaN hetero-interface. The width of the barrier depends on the annealing temperature and duration.

The weak-localization of the two-dimensional electron gas (2DEG) in a modulation-doped Al/sub 0.22/Ga/sub 0.78/N/GaN single quantum well has been investigated through the magnetoresistance measurements. The elastic scattering time /spl tau//sub e/, dephasing time /spl tau//sub /spl phi// and spin-orbit(s-o) scattering time /spl tau//sub so/ at various temperatures are obtained. When the second subband in the triangular quantum well at the heterointerface is occupied by the 2DEG, the anti-weak localization is observed clearly, which is due to the strong spin-orbit interaction. The spin-orbit effect dominates the quantum correction of the conductivity in the upper subband. The intersubband scattering becomes stronger with increasing temperature.

Al content in Al/sub x/Ga/sub 1-x/N/GaN double heterostructure (DH) is improved high up to x=1 by using a compressively strained GaN quantum well (QW) layer. By solving the coupled Schrodinger and Poisson equations self-consistently, we investigate the two-dimensional electron gas (2DEG) distributions and sheet densities in Al/sub x/Ga/sub 1-x/N/GaN DHs. Comparing to the 2DEG in Al/sub 0.5/Ga/sub 0.5/N/GaN single heterostructure (SH), the 2DEG sheet density in a comparable AlN/GaN/Al/sub 0.5/Ga/sub 0.5/N DH is nearly doubled from 2.31/spl times/10/sup 13/cm/sup -3/ to 4.47 /spl times/ 10/sup 13/cm/sup -3/, mainly owing to the additional piezoelectric polarization in the GaN QW. It is also shown that 2DEG in the GaN QW is increased with increasing the Al content of the top barrier due to the stronger polarization effect and large conduction band offset at the Al,Ga/sub 1-x/N/GaN interface. Increasing the lower barrier thickness will reduce the 2DEG density in the GaN QW while the 2DEG at the lower Al/sub y/Ga/sub 1-y/N/GaN interface is increased, making the total 2DEG density almost a constant.

Magnetointersubband scattering (MIS) oscillations of two-dimensional electron gas (2DEG) in unintentionally doped Al/sub 0.22/Ga/sub 0.78/N/GaN heterostructures have been investigated by means of magnetotransport measurements at low temperatures and high magnetic fields. It is found that the MIS oscillations become slightly weaker with increasing temperature and become dominant with increasing temperature. Due to the different temperature dependence between the Shubnikov-de Haas (SdH) and the MIS oscillations, it is observed that the SdH oscillations modulated strongly by the MIS oscillations between 10 K and 17 K while the modulations are very weak at other temperatures.

Magnetotransport properties of modulation-doped Al/sub x/Ga/sub 1-x/N/GaN heterostructures were studied at low temperatures and high magnetic fields. The strong Shubnikov-de Hass oscillations with the double periodicity is clearly observed, indicating the two-dimensional electron gas (2DEG) occupation of the double subbands in the triangular quantum well at the heterointerfaces. It is determined that the 2DEG occupation of the double subbands occurs when the 2DEG sheet concentration reaches 9.0 /spl times/ 10/sup 12/cm/sup -2/, and the energy separation between the first and the second subbands is 75 meV. The quantum scattering time related to the first subband is determined to be 8.4 /spl times/ 10/sup -14/ s. The mobilities of the 2DEG in the first and the second subbands, magnetointersubband scattering oscillations of the 2DEG and the spin splitting of the 2DEG have also been studied.

We have studied the optical properties of the ultraviolet detector based on the GaN epilayer grown on 6H-SiC substrate by metalorganic chemical vapor deposition. We obtained the detectable energy span of the device up to ultraviolet by photocurrent measurement. The spectral responsivity remained nearly constant for wavelengths from 250 to 365 nm and dropped by three orders of magnitude within 10 nm of the band edge (by 380 nm). The detector was measured to have a responsivity of 133 A/W at a wavelength of 360 nm under a 5-V bias, and the voltage-dependent responsivity was performed. Furthermore, an easy method was developed to determine the response time and the relationship between response time and bias was obtained.

The electrical and optical properties of double heterostructure blue light-emitting diodes, with an In/sub 0.06/Ga/sub 0.94/N:Zn,Si active layer, made by Nichia Ltd., were investigated at various temperatures. Measurement of the forward bias current-voltage behavior of the device demonstrates a departure from the Shockley model of p-n diodes, and it is observed that the dominant mechanism of carrier transport across the junction is associated with carrier tunneling. Electroluminescence experiments of the devices indicates that there is an emission peak located at 2.80 eV, and a relatively weaker short-wavelength peak at 3.2 eV. A significant blue shift of the optical emission peak, consistent with the tunneling character of electrical characteristics, was observed. Furthermore, we studied the properties of electroluminescence under various pulsed currents, and a degradation in I-V characteristics and a low resistance ohmic short were observed.

The transient photoconductivity (PC) properties of a GaN thin film on a (0001) sapphire substrate are investigated. The decay curves of PC obtained by a YAG:Nd pulsed laser are divided into two special regions, which are the beginning and tail decay regions, corresponding to two time constants, 0.1 ms and 1.0 ms, respectively. Keeping the same light intensity and bias voltage, when the sample is heated to 300/spl deg/C, the time constants are both reduced. It shows that there are a large number of traps at the position of tens of meV below the conduction band edge. The PC ascends S-shaped when the data are collected during the first 200 ns. As the sample is not shined, the PC sharply reduces and oscillates, indicating that the carriers redistribute between the deep traps and the conduction band. As an approximation, a model involving two trapping levels, shallow and the deep trapping levels, is used to represent the structure of the electron trapping levels in the gap. The simulation based on this model is in good accord with the experimental results. Moreover, the mechanism of the PC curve variation with light intensity is explained by the model.

Epitaxial growth of high quality hexagonal GaN films on sapphire substrates using light radiation heating metal-organic chemical vapor deposition (LRH-MOCVD) is reported. The deposition temperature is 950/spl deg/C, about 100/spl deg/C lower than that in normal rf-heating MOCVD growth. The FWHM of the GaN (0002) peak of X-ray diffraction rocking curve is 9.8 arc min. The photoluminescence spectrum of GaN shows that there is a very strong band-edge emission and no "yellow-band" luminescence. Hall measurement indicates that the n-type background carrier concentration of the GaN film is 1.7/spl times/10/sup 18/ cm/sup -3/ and the Hall mobility is 121.5 cm/sup 2//V.s. It is suggested that the radiation of light in GaN growth enhances the dissociation of ammonia and decreases the disadvantages of the parasitic reaction between trimethylgallium and ammonia.