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The ZnO films were grown by low pressure metal-organic chemical vapor deposition (LP-MOCVD) using dimethylzinc (DMZn) and oxygen. The as-grown film has strong (0002) oriented characteristic, containing the chain-like network grains in small sizes, A well-resolved shoulder emission at 3.03 eV in the photoluminescence (PL) spectra has been ascribed to the interstitial zinc in the crystal, implying a serious oxygen deficiency state of the MOCVD growth, in good agreement with the analysis of XPS results. Post-annealing of the films leads to the remarkable improvement of the structure, morphology, components and optical properties. Large hexagonal columnar grains were then observed by atomic force microscope (AFM). The luminescence efficiency was enhanced greatly due to the reduction of the nonradiative defects. Meanwhile, chemisorbed oxygen gives rise to surface acceptor states, resulting in the different radiative recombination. Photoluminescence excitation measurement shows good agreement with the above conclusions. [ABSTRACT FROM AUTHOR]

Quantum and transport scattering times related to different subbands in modulation-doped Al0.22Ga0.78N/GaN single quantum wells (SQW) have been studied by magneto- transport measurements. The quantum scattering time related to the first and the second subbands is determined to he 0.078 ps and 0.088 ps, respectively, at 1.5 K. Results indicate that the scatterings from heterointerface and ionized donors at both side of GaN well are all important in limiting quantum scattering time. By using mobility spectrum technique the transport scattering time related to the first subband is determined to he 0.128 ps. Transport-to-quantum scattering time ratio in the first subband is 1.6. It is concluded the large angle scatterings play a very important role in limiting quantum scattering time in this SQW. [ABSTRACT FROM AUTHOR]

The GaN-rich side of GaNP ternary alloys has been successfully synthesized by light-radiation heating and low-pressure metal-organic chemical vapor deposition. X-ray diffraction (XRD) rocking curves show that the (0002) peak of GaNP shifts to a smaller angle with increasing P content. From the GaNP photoluminescence (PL) spectra, the red shifts from the band-edge emission of GaN are determined to he 73, 78 and 100 meV, respectively, in the GaNP alloys with the P contents of 1.5%, 5.5% and 7.5%. No PL peak or XRD peak related to GaP is observed, indicating that phase separation induced by the short-range distribution of GaP-rich regions in the GaNP layer has been effectively suppressed. The phase-separation suppression in the GaNP layer is associated with the high growth rate and the quick cooling rate under the given growth conditions, which can efficiently restrain the accumulation of P atoms in the GaNP layer. [ABSTRACT FROM AUTHOR]

ZnO films were prepared on (0002) sapphire by metal-organic chemical vapor deposition (MOCVD) with fixed Zn and O gas flow rates. The film properties displayed complex dependencies on temperature over the range 330–460 °C. All films were preferentially oriented along the (0002) direction and the integrated intensity of the (0002) peak increased with increasing substrate temperature, indicative of an increasing deposition rate. Furthermore, high substrate temperatures promoted the growth of columnar grains, and improved the crystallinity, as the decreasing FWHM of the (0002) ZnO peak suggests. However, it was not the highest temperature sample, but the sample deposited at 390 °C that had the best UV band emission characteristics, with no defect-related luminescence in the photoluminescence (PL) spectra, as well as the highest transmission and sharpest absorption edge in the transmittance spectra. [ABSTRACT FROM AUTHOR]

Abstract. The impact of device scaling on modern MOS technology is discussed in terms of the random telegraph signals (RTSs) and low-frequency noise in n-MOSFETs with gradually decreased channel widths. RTSs with very large amplitude (> 60%) am observed in the devices with ultra-narrow channels at room temperature for the first time. Furthermore, low-frequency noise spectra having both 1/f' and Lorentzian type are found separately in the same ultra-narrow channel at different gate bias voltage, whereas only 1/f' noise is observed in relatively wide channels. The observations strongly suggest that low-frequency noise in weak inversion dominantly suffer from carrier mobility fluctuation rather than carrier number fluctuation in ultra-narrow channels, which is confirmed by numerical simulations. [ABSTRACT FROM AUTHOR]

Abstract. The oxidation of GaN epilayers in dry oxygen has been investigated. The GaN epilayers, about 1 micro m thick, were grown on (0001) sapphire substrates by rapid thermal process/low pressure metalorganic chemical vapor deposition. Bulk theta - 2 theta X-ray diffraction (XRD) data showed that the slight oxidation of GaN began to occur at 800 Celsius tot 6 h. The oxide was identified as the monoclinic beta-Ga[sub 2]O[sub 3]. The GaN epilayers were completely oxidized at 1050 Celsius for 4 h or at 1100 Celsius for I h. For all samples, the strongest oxide's peak is (11-3), and (30-6) followed. There is a rapid oxidation process in the initial stage of oxidation, and a relatively slow process followed when the temperature was over 1000 Celsius. The oxidation of two stages was limited by the rate of an interracial reaction mechanism and by the diffusion mechanism, respectively. When the temperature reaches 1100 Celsius, the oxidation rate is very fast, which is considered as the results of the GaN decomposition at high temperature under atmosphere. The oxide layers were also observed by a scanning electron microscope, which shows a rough oxide surface and an expansion of the volume of 40%. The photoluminescence (PL) seriously influenced by the oxidation is also discussed. [ABSTRACT FROM AUTHOR]

Abstract. Epitaxial growth of high-quality hexagonal GaN films on sapphire substrates using light-radiation heating metal-organic chemical vapor deposition (LRH-MOCVD) is first reported. The deposition temperature is 950 Celsius, about 100 Celsius lower than that in normal rf-heating MOCVD growth. The FWHM of GaN (0002) peak of the X-ray diffraction rocking curve is 8.7 arc min. Photoluminescence spectrum of GaN film 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 GaN film is 1.7 x 10[sup 18]cm[sup -3] and the Hall mobility of it 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 parasite reaction between trimethylgallium and ammonia. [ABSTRACT FROM AUTHOR]

Abstract. Thin heteroepitaxial films of Si[sub 1-x-y]Ge[sub x]C[sub y] have been grown on Si(100) substrates by rapid thermal chemical vapor deposition (RTCVD) using C[sub 2]H[sub 4] as C source. The composition and microstructure of Si[sub 1-x-y]Ge[sub x]C[sub y] films were characterized by Auger electron spectroscopy, Raman spectra and Fourier-transform infrared spectroscopy. The results show that lower temperature and higher SiH[sub 4]/C[sub 2]H[sub 4] flow ratio are helpful in forming the substitutional C and improving the crystal quality. A possible mechanism for C incorporation in Si[sub 1-x-y]Ge[sub x]C[sub y] layers grown by RTCVD using C[sub 2]H[sub 4] is proposed. [ABSTRACT FROM AUTHOR]

Abstract. The transient photoconductivity (PC) properties of GaN thin film on (0001) sapphire substrate are investigated. The decay curves of PC obtained by 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 Celsius, 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 illuminated, 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, the shallow and the deep trapping levels represents the structure of the electron trapping levels in the gap. The simulation based on this model is well in accordance with the experimental results. Moreover, the mechanism of how the PC curves varied as the light intensity is explained by the model. [ABSTRACT FROM AUTHOR]

Raman scattering from an AlGaN/GaN heterostructure was performed in the temperature range from 77 to 773 K. The first- and second-order Raman scattering of the A1 longitudinal-optical phonon-plasmon coupled mode from an AlGaN/GaN interface as well as the Raman scattering from the GaN layer were observed. All the modes downshift, and their intensities weaken with increasing temperature. The free-carrier concentration estimated by the frequency of the coupled mode from an AlGaN/GaN interface is 7.5 times as high as that of n-AlGaN, indicating mass free-carrier transfer from the AlGaN barrier to the GaN well. Moreover, the temperature dependence of the phonon frequency is well described by an empirical formula. [ABSTRACT FROM AUTHOR]

In this letter, we investigate the carrier features in AlGaN/InGaN/GaN heterostructure field-effect transistors. A study of charge control in the AlGaN/InGaN/GaN structure is performed by self-consistently solving Schrödinger's equation in conjunction with Poisson's equation. The results indicate that the concentration of two-dimensional electron gas can be largely increased with the incorporation of an InGaN layer. Both carrier density and quantum confinement are very sensitive to the strain in the InGaN channel layer. These novel features are attributed to the strong polarization effect in the AlGaN/InGaN and InGaN/GaN interfaces. [ABSTRACT FROM AUTHOR]

Room-temperature photoluminescence spectra of Mg-implanted GaN grown on sapphire by low-pressure metal-organic chemical vapor deposition have been studied. An obvious blue emission and a broad yellow-band emission were observed. Spectra analysis suggests that, in the forbidden band of GaN, there exist four doping-related energy levels at 170 meV and 310 meV below the conduction band, and at 250 meV and 390 meV above the valence band, respectively. Transitions between these energy levels give the blue emission of 415 nm and 438 nm. Also, annealing partially recovers the GaN crystalline structure, leading to the reappearance of the yellow-band luminescence. [ABSTRACT FROM AUTHOR]

The two-dimensional electron gas distribution in AlGaN/GaN high electron mobility transistors is determined from the solution of the coupled Schrödinger’s and Poisson’s equations. Considering the piezoelectric effect, the two-dimensional electron gas concentration is calculated to be as high as 7.7×10[sup 19] cm[sup -3] . In order to obtain an understanding of how the two-dimensional electron gas distribution is influenced by dopants in GaN, we observed the two-dimensional electron gas concentration and occupation of sub-bands versus dopant concentration in the GaN layer of an AlGaN/GaN heterostructure. Our results show that the two-dimensional electron gas concentration is slightly increased at higher doping levels in GaN, while the quantum confinement in the AlGaN/GaN heterostructure is weakened with the increase of donor concentration in the GaN layer. [ABSTRACT FROM AUTHOR]

Abstract. Si-based metal-ferroelectric-semiconductor (MFS) structures without buffer layers between Si and ferroelectric films have been developed by depositing SrBi[sub 2]Ta[sub 2]O[sub 9] (SBT) directly on n-type (100)-oriented Si. Some effective processes are adopted to improve the electrical properties of these MFS structures. Contrary to the conventional MFS structures with top electrodes directly on ferroelectrics, our MFS structures have been developed with thin dense SiO[sub 2] films deposited between ferroelectric films and top electrodes. Due to the SiO[sub 2] films, the leakage current densities of MFS structures are reduced to 2 x 10[sup -8] A/cm[sup 2] under the bias of 5 V. The C - V electrical properties of the MFS structures are greatly improved after annealing at 400 Celsius in N[sub 2] ambient for 1 h. The C - V memory windows are increased to 3 V, which probably results from the decrease of the interface trap density at the Si/SBT interface. [ABSTRACT FROM AUTHOR]

Abstract. Ge-rich Ge[sub 1-x-y]Si[sub x]C[sub y] alloys have been grown on Si (100) substrates by plasma-enhanced rapid thermal chemical vapor deposition. It is found that there is a strong suppressive effect of C on the Ge composition and the growth rate. A possible mechanism for the suppressive effect is proposed. After calculations of atomic configuration, we obtain the relationship between the degree of suppression and the Ge/C atomic ratio. From the calculation results, a saturation tendency of the suppressive effect is expected with increasing Ge concentration in the growth of Ge[sub l-x-y]Si[sub x]C[sub y] alloys. [ABSTRACT FROM AUTHOR]

Abstract. Pentagon-shaped silicon wires with linewidth around 300nm are successfully fabricated by using the Si/SiGe epitaxy technique, reactive ion etching, and subsequent selective chemical etching. The nanowires are oxidized in wet O[sub 2] at 750 Celsius and 850 Celsius. The oxide and interface morphology are characterized by cross-sectional scanning electron microscope images. It is found that the oxidized nanowire following oxidation at 750 Celsius still keeps its pentagon shape even if it has been oxidized for 19 h. However, the oxidized samples at 850 Celsius become circular in shape. The oxidation-temperature dependence of the sample shapes is discussed. Our results should be useful in generating silicon nanowires coated with SiO[sub 2] in microelectronic technology with careful selection of the SiO[sub 2] growth temperatures. [ABSTRACT FROM AUTHOR]