Béla Szentpáli

Evaluation of InP-to-silicon heterobonding

Abstract In this paper, we evaluate hydrophilic (HP) and hydrophobic (HB) surface pre-treatments in InP-to-Si direct wafer bonding. Surface roughness and surface chemistry was examined using atomic force microscopy and X-ray photoelectron spectroscopy, respectively. After bonding, the bonded interfaces were evaluated using infrared transmission imaging, bond-strength and current–voltage (I–V) measurements. It was found that HP surface treatment using oxygen plasma makes room temperature bonding of InP and Si very spontaneous, and results in high bond-strengths already after low-temperature annealing. This was not observed when using standard oxidising acids as HP surface treatment before bonding. HB InP and Si surfaces, also, did not prove to bond spontaneously at room temperature and the bond-strength started to increase only after annealing at about 400°C. HB bonding and annealing at 400°C was though the best choice regarding the electrical characteristics of the bonded InP/Si heterojunction.

Thermopile antennas for detection of millimeter waves

A thermopile structure is proposed for the detection of microwave/millimeter wave radiation. The thermopairs in the suggested linear arrangement function as antennas. 5.58 V/W responsivity was achieved at 100 GHz with 40 serial connected thermopairs. The experimentally observed polarity and frequency dependence convincingly verify the proper detector operation.

Tunneling in planar‐doped barrier diodes

The effect of the thermionic‐field emission mechanism on the I‐V characteristics of planar‐doped barrier diodes is investigated. The regions of temperature and of structural dimensions are given where this effect appears. The differences due to the different shapes of the potential barrier are pointed out between planar‐doped barrier diodes and Schottky diodes.

Noise in piezoresistive Si pressure sensors

The principles of the construction of piezoresistive silicone pressure sensors are outlined. The fabrication of sensors with ion-implantation and common silicone wafer technology is described. The simulation of the devices showed that the membrane thickness has a major influence on the sensitivity, while the misalignment is less important. The low-frequency noise spectra of the piezoresistive elements are Lorenzian; the characteristic time constant is about 23 μs. The bias dependence of the spectra is in some degree less than it was expected from the regular V2 scaling. The plateau of the noise spectrum at working conditions is higher with almost 30 dB than the thermal noise. This excess noise is attributed to a trap level; however the origin of this G-R center is not clear yet. The figures of merits of the sensor were also estimated in numerical examples.

Engineered Schottky barriers on n-In0.35Ga0.65As

The Schottky barrier height in Al/n-In 0 35 Ga 0.65 As was engineered using thin p-type near-interface In 0.35 Ga 0.65 As layers grown by molecular beam epitaxy. The effect of the thickness and doping level of the p-type layer on the barrier height was also studied by computer simulation. A good agreement was obtained between the calculated and experimental barrier height values. An experimental Schottky barrier height of 0.67 eV with an ideality factor of 1.15 has been achieved.

I-V characterisation of resonant tunneling diodes

The current-voltage characteristics of AlAs/GaAs resonant tunnelling diodes are measured in steady state circumstances and by a new method in the submicrosecond time scale. The results show that I-V characteristics are sensitive to the measuring time due to internal transient of the device. The internal transients are identified as thermal transients and as charge accumulation at the barriers and in localised electronic states. It is concluded that a reliable I-V characterisation of these devices is possible only when the results measured by different methods is compared and analysed properly.

Low-frequency noise in porous Si LED

The current-voltage characteristics and the low-frequency noise spectra of p-type Si - Porous Si - Al light emitting diodes were investigated. over 1 V forward biases a reasonable fit was obtained in the Fowler-Nordheim plot. At lower biases, however, an additional current-component appears, which shows a saturating character. This current component is ascribed to trap-assisted tunneling. Any attempts of accurately fitting the I-V characteristic by other known transport mechanisms failed, as reported earlier. The measured noise spectra show 1/f character. While the biasing current was varied from a about 30 microAmps up to several mAs, the noise level remained constant within the measuring error, i.e. the voltage noise is independent of the bias. This is contradictory to the results obtained on uniform resistors, where the noise power scales with I2, or V2. On this reason the observed noise is attributed to the saturating trap-assisted tunneling.

THz detection by modified thermopile

The modified micromachined thermopile consists of linearly arranged thermopairs instead of the usual loops. This device can act as a series of antennas and senses the millimeter wave radiation [1]. The antenna-like operation was demonstrated by the strong dependence on the polarization. The working principle is similar to the bolometers in that respect that the absorbed radiation heats up the semiconductor strips, but the temperature increment is sensed by the Seebeck effect instead of the resistance increment. Therefore there is no read-out current and the voltage output starts from zero. In the present work we are going to search absorption spectra of the device. It is shown that the resonance depends mainly on the dimensions and shape of the chip; the linear thermopiles are rather E-field probes. The fabrication of the device will be also outlined as well as the experimental results.

ANOMALOUS BIAS DEPENDENCE OF THE NOISE IN POROUS SI LED

The current-voltage characteristics and the low-frequency noise spectra of p-type Si–Porous Si–Al diode like structures were investigated. Over 1 V forward biases a reasonable fit was obtained in the Fowler-Nordheim plot. Any attempts of accurately fitting the I-V characteristic by other known transport mechanisms failed. At lower biases, however, an additional current-component appears which shows a saturating character. This current component is ascribed to trap-assisted tunneling. The measured noise spectra show 1/f character; however the magnitude of the noise shows saturation with increasing biases instead of the usual case, where the noise power scales with I2, or V2. This finding is interpreted by a model of two parallel current paths. The noise arising from the smaller and saturating current determines the noise performance of the whole device.

GaAs planar doped barrier diodes

Abstract The planar doped barrier diodes are majority carrier devices with technologically controlled barrier height. This paper reviews the main current conducting mechanisms. The limits of the I–V characteristics are described. The design of the device is shown on an example. The measured and calculated characteristics agree well.