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Photoluminescence (PL), X-ray diffraction (XRD) and Raman spectra have been measured to characterize the effects of phosphorus on the optical and structural properties of GaN1−xPx alloys with x&les;15%, grown by means of light-radiation heating, low-pressure metal-organic chemical vapor deposition. The PL spectra of GaN1−xPx show the largest red shift of 100 meV from the band-edge emission of GaN. XRD rocking curves show that the (0 0 0 2) peak of GaN1−xPx shifts to smaller angles with increasing P content. The Raman spectra of GaN1−xPx, recorded in backscattering geometry, exhibit four new vibrational modes at 256, 314, 377 and 428 cm−1 compared with an undoped GaN sample. The modes at 377 and 428 cm−1 are attributed to gap modes related to the Ga–P bond vibrations, whereas the other two modes at 256 and 314 cm−1 are assigned to phosphorus clusters and disorder-activated scattering, respectively. The frequency of the A1 (LO) mode is found to decrease with increasing x at a much high rate of approximately 268 cm−1/x for x<0.03. This red shift is attributed to the effects of alloying and strain. Furthermore, we have not observed characterizations related to GaP resulted from the phase separation from PL, XRD and Raman spectra of all investigated GaN1−xPx samples. [Copyright &y& Elsevier]

Pt/Au Schottky contacts were fabricated on modulation-doped Al0.22GaN0.78/GaN heterostructures. Some different surface treatments were used before the deposition of the metal contacts to prevent the formation of the native oxide layer on the samples’ surfaces. Comparing the barrier height and the ideal factor of the Schottky contacts, we found that the treatment of the boiling (NH4)2S solution can remove the native oxide layer effectively. Detailed X-ray photoelectron spectroscopy measurements were also made to investigate the chemical reactions on the surface of samples after different treatments. [Copyright &y& Elsevier]

The evolution of wing tilt in laterally and epitaxially overgrown (LEO) GaN thick film was studied using cross-sectional transmission electron microscope (TEM) observation and high-resolution X-ray diffraction (XRD). The LEO GaN film was grown by hydride vapor epitaxy (HVPE) on Si(1 1 1) substrate. Horizontally propagating dislocations (HDs) and low density of threading dislocation (TD) in LEO wings were observed in TEM micrographs. Tilt of LEO wing to the GaN seed region was measured as 3.3° at interface of HVPE–GaN/metal organic vapor phase epitaxy (MOVPE)–GaN by selective area electron diffraction, which is much more than that in the surface region estimated as 0.4° by XRD measurements. With φ-scan XRD technique, we found that there exist many differences of tilts and twists of c-axis between the opposite wings on each mask. Asymmetry growth of the opposite wings on SiO2 mask may be due to the flow asymmetry of precursor in vertical reactor. The tilting generation and diminishing increasing with film thickness was discussed too. [Copyright &y& Elsevier]

In this paper, the interface structure of GaN/α-Al2O3 (0 0 0 1) is studied by high-resolution transmission electron microscopy on tilted samples around the 〈1 1 2¯ 0〉Al2O3 axis. Sets of moire´ fringes are observed. There are many disparities, such as contrast, period, tilt angle, and so on, among these moire´ fringes located in different regions. These fringes represent magnifying images of the plane distances of (1 1¯ 0 0)GaN and the tilts of c-axis of GaN crystallites to that of the substrate. According to these results, the growth mechanism of GaN buffer layer at the interface is discussed. [Copyright &y& Elsevier]

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. 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]

Abstract: The LiNbO 3 thin films are successfully grown by pulsed-laser deposition on theAl 0.28 Ga 0.72 N/GaN substrate. The films are characterized by the X-ray diffraction and the X-ray photoelectron spectroscopy. The ferroelectric properties are measured by the piezoresponse force microscopy. An Al/SiO 2 /LiNbO 3 /Al 0.28 Ga 0.72 N/GaN structure is then fabricated and measured by high frequency capacitance–voltage at 1MHz. The mechanism of interaction between interfaces is revealed. [Copyright &y& Elsevier]

Abstract: The high-temperature characteristics of strain in Al0.22Ga0.78N layers, with and without a Si3N4 passivation layer, were investigated at temperatures from room temperature to 813 K by means of high-resolution X-ray diffraction. The results show that a small temperature-dependent strain relaxation occurs in the unpassivated Al0.22Ga0.78N layers when the temperature exceeds 523 K. After passivating, an additional tensile strain and an initial increase of the in-plane tensile strain with increasing temperature were observed in Al0.22Ga0.78N layers, and at higher temperatures the in-plane tensile strain only decreases slightly in the 100-nm-thick Al0.22Ga0.78N layer, but a pronounced temperature-dependent strain relaxation occurs in the 50-nm-thick one due to the fact that the thickness of the Al0.22Ga0.78N layer is close to the critical thickness, and hence the increase of tensile strain induced by passivation will result in partial strain relaxation via the formation of cracks or the glide motion and multiplication of dislocations. [Copyright &y& Elsevier]

Abstract: By using chemical vapor deposition method, 4H-SiC films have been grown on AlN/Si(100) complex substrates at the temperature below 1100 °C. Substitutional Al and N are found in the SiC film. Photoluminescence (PL) peaks, related to Al acceptor and N shallow donor, respectively, have been observed at the room-temperature. The higher partial pressure ratio of SiH4 and C2H4 (P C2H4 / P SiH4 ≧1.62) results in more Si-vacancy (V Si) in the film. The PL peak related to the V Si acceptor level is also observed. [Copyright &y& Elsevier]

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]

Transport properties of the two-dimensional electron gas (2DEG) in AlxGa1−xN/GaN heterostructures were investigated by means of magnetotransport measurements. The mobilities corresponding to the 2DEG in the first and the second subbands in the trianglar quantum well at the heterointerface were obtained. When the AlxGa1−xN barrier is partially relaxed, the mobility of the 2DEG in the first subband decreases significantly, but there is an increase of mobility in the second subband. We suggest that the scattering from the piezoelectric polarization field modulated by the misfit dislocations at the heterointerface is responsible for the decrease of the 2DEG mobility. Meanwhile, the 2DEG in the second subband leaves farther from the heterointerface than that in the first subband, and thus suffers weaker scattering from the heterointerface roughness and the modulated polarization field. Therefore, the mobility of the 2DEG in the second subband is much higher than that in the first subband. [Copyright &y& Elsevier]

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. 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]