A column-base InP lateral bipolar transistor

An InP lateral bipolar transistor has been successfully fabricated on a semi-insulating substrate by implanting Si⁺ as the emitter and collector contacts and Mg⁺ as the column base. An array of 33 1-μm-diameter columns with 1-μm separation between each was formed between the emitter-collector spacing of 3 μm. A current gain of 290 was obtained at 77 K; it was over 12 at room temperature     

Dependence of Hooge parameter of InAs heterostructure on temperature

The InAs quantum well heterostructure was successfully grown on a semi-insulating GaAs substrate by MBE. On the GaAs substrate, the semi-insulating AlGaAsSb was grown to a thickness of 600 nm as the buffer layer, followed by a 15 nm InAs channel layer and a 35 nm AlGaAsSb doped layer together with 10 nm GaAsSb cap layer successively. The electron mobility and the sheet carrier concentration of the 15 nm InAs heterostructure was about 1 m² V⁻¹ s⁻¹ and 4.5×10¹² cm⁻², respectively, at room temperature. This heterostructure is equivalent to the heavily doped InAs substrate with little change of the electron mobility on temperature. This device has typical 1/f noise characteristics without any large bulge throughout the frequency and the temperature ranges observed. The Hooge parameter was α_H=1×10⁻³ at room temperature, decreasing monotonically with the decreasing temperature down to 5×10⁻⁴ at 50 K, indicating characteristics of the virtually constant mobility and constant carrier concentration device.     

Very high electron mobility In0.8Ga0.2As heterostructure grown by molecular beam epitaxy

A very high electron mobility pseudomorphic In_0.8Ga_0.2As heterostructure is successfully grown on InP both by the elimination of the overshoot of flux densities and by the precise control of the flux ratio through a new calibration technique of RHEED oscillations in an MBE system. The critical layer thickness for the pseudomorphic growth of InGaAs on InP is found to follow the energy balance model, and a very high 2DEG mobility of over 1.5 and 16 m²/Vs at 293 and 10 K, respectively, is obtained.     

1/f noise in GaAs filaments

A typical 1/f noise is excited in GaAs filament with the Hooge noise parameter of about α_H=2×10^-3 . The noise level increases in proportion to the square of the terminal voltage, and decreases approximately in inverse proportion to the total number of carriers within the device. A transition from the typical 1/f noise characteristics to the diffusion noise characteristics of MESFETs was observed when the electric field was increased above 1 kV/cm. The noise parameters were also investigated as a function of the device width between 2 and 200 μm. Deep levels within the n-GaAs active layer and the high electric field are the main factors of the nonideal 1/f characteristics     

Noise and transport characterisation of tantalum capacitors

A low frequency noise and charge carrier transport mechanisms were investigated on tantalum capacitors made by various producers. The model of Ta–Ta₂O₅–MnO₂ MIS structure was used to give physical interpretation of I–V characteristics in normal and reverse modes. The noise in time and frequency domain was examined and noise sources were identified. We evaluated correlation between leakage current and noise spectral density and discussed corresponding quality and reliability indicators.     

Interface structural defects and photoluminescence properties of epitaxial GaN and AlGaN/GaN layers grown on sapphire

Overall characterization of the GaN and AlGaN/GaN epitaxial layers by X-ray diffractometry and optical spectral analysis is carried out. The layers are grown by metalloorganic gas-phase epitaxy on (0001)-oriented single crystal sapphire wafers. The components of strains and the density of dislocations are determined. The effects of strains and dislocations on the photoluminescence intensity and spectra are studied. The results allow better understanding of the nature and mechanisms of the formation of defects in the epitaxial AlGaN/GaN heterostructures.     

Hooge fluctuation parameter of semiconductor microstructures

The Hooge 1/f fluctuation parameter α_H of a mesoscopic n-GaAs filament is studied experimentally and compared with that derived from the quantum model. The minimum value of the Hooge parameter α_H was 2×10^-6 and 1×10 ^-8 at room temperature and 60 K, respectively. The temperature dependence of α_H below 100 K and the electric field dependence at 77 K are favorably compared with those obtained for the impurity scattering fluctuation of the quantum 1/f noise theory