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GaN high electron mobility transistors (HEMTs) were monolithically integrated with silicon CMOS to create a functional current mirror circuit. The integrated circuit was fabricated on 100 mm diameter modified silicon-on-insulator (SOI) wafers incorporating a resistive (111) silicon handle substrate and a lightly doped (100) silicon device layer. In a CMOS-first process, the CMOS was fabricated using the (100) device layer. Subsequently GaN was grown by plasma molecular beam epitaxy in windows on the (111) handle substrate surface without wire growth despite using gallium-rich growth conditions. Transmission lines fabricated on the GaN buffer/SOI wafer exhibited a microwave loss of less than 0.2 dB/mm up to 35 GHz. Direct current measurements on GaN HEMTs yielded a current density of 1.0 A/mm and transconductance of 270 mS/mm. At 10 GHz and a drain bias of 28 V, 1.25 mm long transistors demonstrated a small signal gain of 10.7 dB and a maximum power added efficiency of 53% with a concomitant power of 5.6 W. The silicon and GaN transistors were interconnected to form high yield test interconnect daisy chains and a monolithic current mirror circuit. The CMOS output drain current controlled the GaN transistor quiescent current and consequently the microwave gain. [ABSTRACT FROM AUTHOR]

GaN high electron mobility transistor (HEMT) structures have been grown by plasma molecular beam epitaxy on 100 mm diameter (111) silicon substrates. Crack-free films with thicknesses of up to 1.7 (m were deposited without the use of strain-relaxing buffer layers. X-ray measurements indicate high structural uniformity and the Pendellosung oscillations are observed due to the abruptness of the AlGaN/GaN interface. Capacitance-voltage measurements display a sharp pinch-off with a depleted GaN buffer layer and no measurable charge accumulation at the substrate-epi interface. Transmission line measurements on the GaN HEMT buffer and substrate indicate a loss of less than 0.2 dB/mm up to 20 GHz. An average sheet resistance of 443 )/sq with a standard deviation of 0.8% and a mobility of 1600 cm2 /V s were obtained for an Al0.25Ga0.75N/GaN HEMT. Transistors were fabricated with a current density of 1.2 A/mm and a transconductance of 290 mS/mm which is quite comparable to GaN HEMTs on SiC [ABSTRACT FROM AUTHOR]

Homoepitaxial growths of ZnO were performed by low pressure metal organic chemical vapor deposition (MOCVD) on both bulk hydrothermal and thin film buffer layers of ZnO grown by pulsed laser deposition on c-sapphire substrates. The surface roughness, photoluminescence, and x-ray diffraction (0002) peak omega rocking-curve line widths for the bulk and thin film substrates were similar prior to MOCVD growth. After MOCVD growth, it was found that the surface morphology, crystallographic quality, and optical properties of the ZnO layers were far superior to those typically observed for heteroepitaxial growth of ZnO layers on c-sapphire by MOCVD. The MOCVD layers were comparable for growths on both the bulk substrate and the thin film buffer layer. Furthermore, no significant impact of carrier gas was observed. The quality of the ZnO layer appeared to be correlated with the surface morphology and the crystalline quality of the substrate rather than being dependent on whether the substrate was in bulk or thin film form. [ABSTRACT FROM AUTHOR]

Nitrogen-doped ZnO films were grown by metal organic chemical vapor deposition using diallylamine as the doping source. Secondary ion mass spectrometry measurements attest for the incorporation of nitrogen up to 1020 cm-3, and both photoluminescence and Raman characterization exhibit nitrogen related peaks. As-deposited layers have been characterized by Hall effect, and most exhibit n-type conductivity, with electron concentrations from 1017 up to a few 1019 cm-3. Unstable p-type behavior is sometimes observed on low quality layers grown using a very low RVI/II ratio. Ex situ annealing experiments in oxygen atmosphere show different tendencies depending on the growth conditions and can lead to a strong decrease in the electron concentration by three orders of magnitude. These results are discussed in relation to the structural and optical characterizations. [ABSTRACT FROM AUTHOR]

Pt Schottky diodes were formed on single ZnO nanowires grown by site-selective molecular-beam epitaxy and then transferred to SiO2-coated Si substrates. The diodes exhibit excellent ideality factors of 1.1 at 25 °C and very low (1.5×10-10 A, equivalent to 2.35 A cm-2, at -10 V) reverse currents. The nanowire diodes show a strong photoresponse, with the current–voltage characteristics becoming ohmic under ultraviolet illumination (366 nm light). The on-off current ratio of the diodes at 0.15/-5 V was ∼6. These results show the ability to manipulate the electron transport in nanoscale ZnO devices. [ABSTRACT FROM AUTHOR]

The electrical characteristics of Zn0.9Mg0.1O/ZnO p–n junctions grown by pulsed-laser deposition on bulk, single-crystal ZnO substrates are reported. The forward turn-on voltage of the junctions was in the range 3.6–4 V for Pt/Au metallization used for the p-Ohmic contact on Zn0.9Mg0.1O.The reverse breakdown voltage is as high as 9 V, but displays a small negative temperature coefficient of -0.1–0.2 V K-1 over the range 30–200°C. The achievement of acceptable rectification in the junctions required growth of an n-type ZnO buffer on the ZnO substrate prior to growth of the p-type, phosphorus-doped Zn0.9mg0.1O.Without this buffer, the junctions showed very high leakage current. [ABSTRACT FROM AUTHOR]

The Schottky barrier height of Pt contacts on n-type (n∼1016 cm-3) thin film ZnO deposited by pulsed laser deposition was obtained from current–voltage measurements as a function of temperature. The resulting values ranged from 0.61±0.04 eV at 25 °C to 0.46±0.06 eV at 100 °C with saturation current densities of 1.5×10-4 A cm-2 (25 °C) to 6.0×10-2 A cm-2 (100 °C), respectively. The reverse current magnitude was larger than predicted by thermionic emission alone. The measured barrier height for Pt on ZnO is similar to the value reported for both Au and Ag rectifying contacts on this material. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Pt Schottky rectifier arrays were fabricated on 200-μm-thick, freestanding GaN layers. Even with the reduced dislocation density in these layers (∼10[sup 5] cm[sup -2]) relative to conventional GaN on sapphire (>10[sup 8] cm[sup -2]), rectifiers fabricated on the freestanding GaN show a strong dependence of reverse breakdown on contact diameter. We show that by interconnecting the output of many (∼130) smaller (500 μm×500 μm) rectifiers, we can achieve high total forward output current (161 A at 7.12 V), low forward turn-on voltage of ∼3 V, and maintain the reverse breakdown voltage. The on/off ratio of the rectifier array was ∼8×10[sup 7] at 5 V/-100 V. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

GaAs pseudomorphic high electron mobility transistor (PHEMT) structures were grown by molecular beam epitaxy on germanium substrates and composite silicon template wafers incorporating silicon and germanium transferred layers. Windows were etched down to the buried germanium layer and subsequent blanket material growth resulted in single crystal growth in the windows and polycrystalline growth on the top SiO2 surface. Wire growth was eliminated at the window edges and on the top SiO2 surface. Secondary ion mass spectrometry measurements and transmission electron micrographs of GaAs grown on germanium indicated an abrupt GaAs–Ge interface with little penetration of antiphase boundaries or other defects into the GaAs layer. For PHEMT material grown on silicon template wafers, a surface roughness of 8 Å was measured by atomic force microscopy. The room temperature photoluminescence intensity of the InGaAs channel in the PHEMT structure was equivalent to that grown on GaAs substrates. Measured PHEMT mobilities and sheet densities were comparable to those obtained on GaAs substrates. Transistors were fabricated with 0.25 μm gates. The maximum dc current density, 520 mA/mm, and transconductance, 360 mS/mm, were very similar to devices fabricated on GaAs substrates. [ABSTRACT FROM AUTHOR]

We have demonstrated a functional P-n-p heterojunction bipolar transistor (HBT) using InGaAsN. The metalorganic-vapor-phase-epitaxy-grown Al[sub 0.3]Ga[sub 0.7]As/In[sub 0.03]Ga[sub 0.97]As[sub 0.99]N[sub 0.01] HBT takes advantage of the narrower band gap energy (E[sub g]=1.2 eV) of In[sub 0.03]Ga[sub 0.97]As[sub 0.99]N[sub 0.01], which is lattice matched to GaAs. Compared with the Al[sub 0.3]Ga[sub 0.7]As/GaAs material system, the Al[sub 0.3]Ga[sub 0.7]As/In[sub 0.03]Ga[sub 0.97]As[sub 0.99]N[sub 0.01] material system has a larger conduction-band offset, while the valence-band offset remains comparable. This characteristic band alignment is very suitable for P-n-p HBT applications. The device's peak current gain is 23, and it has a turn-on voltage of 0.77 V, which is 0.25 V lower than in a comparable P-n-p Al[sub 0.3]Ga[sub 0.7]As/GaAs HBT. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The improvement of identification accuracy of concurrent vowels with differences in fundamental frequency (delta F0) is usually attributed to mechanisms that exploit harmonic structure. To decide whether identification is aided primarily by selecting the target vowel on the basis of its harmonic structure ("harmonic enhancement") or removing the interfering vowel on the basis of its harmonic structure ("harmonic cancellation"), pairs of synthetic vowels, each of which was either harmonic or inharmonic, were presented to listeners for identification. Responses for each vowel were scored according to the vowel's harmonicity and that of the vowel that accompanied it. For a given target, identification was better by about 3% for a harmonic ground unless the target was also harmonic with the same F0. This supports the cancellation hypothesis. Identification was worse for harmonic than for inharmonic targets by 3%-8%. This does not support the enhancement hypothesis. When both vowels were harmonic, identification was better by about 6% when the F0's differed by 1/2 semitone, consistent with previous experiments. Results are interpreted in terms of harmonic enhancement and harmonic cancellation, and alternative explanations such as waveform interaction are considered.