Saburo Yokokura

Electron Cyclotron Resonance Plasma Etching of n-SiC and Evaluation of Ni/n-SiC Contacts by Current Noise Measurements

The Si surface of n-SiC is etched by an Ar electron cyclotron resonance plasma in order to smooth the as-received substrates. Low-frequency current noise characteristics of Ohmic contacts of the wide-band-gap semiconductor n-SiC are investigated. Ohmic contacts with a diameter of 200 µm have a minimum Ohmic contact resistance of the order of 10-4 Ωcm2 at an alloying temperature of 1000°C for 30 min. These low resistance Ohmic contacts show typical 1/f current noise characteristics that increase with the square of the sample current I2. A sample with a higher contact resistance exhibits, however, current noise power increase with increasing sample current I. The relevant total electron number between the electrodes of the bulk substrate is estimated from the resistance and by finite element method simulation, from which the Hooge parameter αH is estimated to be approximately 40.

Dependence of Hooge constant on mean free paths of materials

The Hooge parameters of compound semiconductors are found to be in inverse proportional to the mean free paths of materials. The newly developed model of 1/f phonon energy partition fluctuation in thermal equilibrium predicts the value of Hooge parameter as αH = a/λ, the ratio of the lattice constant a and the mean free path λ. Several reported experimental results on αH for very pure semiconductors are found on the a/λ line. Experimental verification is given by measuring noise in InGaAs/InAlAs heterostructure, where optical phonon effects can be observed due to negligible impurity scattering. The Hooge parameter of about 1 in p-InGaAs and 10-3 to 10-5 in n-InGaAs reflects the two order difference in the mobility and corresponding λ values.

New Tools For Fast And Senstive Noise Measurements

An instrument to improve power spectrum density (PSD) measurements, a highly sensitive preamplifier and a data acquisition unit are designed as well as a programmable power battery source. The preamplifier has 8 junction field effect transistor (JFET) inputs in parallel resulting in an input noise equivalent power of —186 dBV2/Hz. The data acquisition system consists of a low-pass filter, an A/D converter and a RAM, which transfer the data to the connected PC. The FFT or other signal processing is carried out within the PC. The battery power source is controlled by the PC, enabling us to obtain the device-under-test (DUT) bias DC required by the program. This measuring system works well at room temperature where the DUT and the power source could be put into a magnetic shielding box to reject spurious line noises. In the case where the DUT is placed in a cryostat to measure the temperature dependence of noise properties, however, the shielding of the DUT from the power line becomes a serious problem. Particularly in order to use a compressor cooling system, spurious noises come into the measuring system through the power lines of the compressor. In such a case the preamplifier must be placed as close as possible to the DUT, and the power line to the compressor is sometimes disconnected from the system.

Low-Frequency Noise Measurements as a Quality Indicator for Ohmic Contacts to n-GaN

Ohmic contacts to n-GaN are evaluated by low frequency noise mea surements. Ohmic contacts were formed by electron beam evaporation of Ti/Al and their rapid thermal alloying. The electron cyclotron resonance Ar plasma etched surface has a poor Ohm ic contact with a typical contact resistance of 8.1 × 0 Ω⋅cm, while the as received surface had a better Ohmic contact with a lower contact resistance of 7.5 ×10 Ω⋅cm. The Ohmic characteristics are monitored by the 1/ f noise measurements. Low resistance contacts give the typical 1/ f noise characteristics, the amplitude of which increases with the square of the sample current I, while high resistance contacts give the linear noise power dependence on the sample current I. We are able to evaluate, therefore, the quality of the electrodes most sensitive by the 1/ f noise measurements. Assuming the relevant electron concentration between the electrodes, the Hooge parameter is estim at d as αH = 5.3×10 -6 at room temperature.

Evaluation of Al/Ti/n-GaN Contacts by Current Noise Measurements

Ohmic contacts are formed on the epitaxial n-GaN film by the electron beam evaporation of Ti/Al and their rapid thermal alloying with device separation by a fairly fast Electron Cyclotron Resonance (ECR) plasma etching. The etched surface has a poor ohmic contact with a typical contact resistance of 8.1 × 10 - 3 Ω.cm 2 , while the as-received and rinsed surface has a better contact with a lower contact resistance of 7.5 × 10 - 6 Ω.cm 2 . The resistivity of the film is determined as a function of the temperature, in good agreement with the numerical analyses. The ohmic characteristics are evaluated by the 1/f noise measurements. Low ohmic contacts give the typical 1/f noise characteristics which increase with the square of the sample current 1, while higher ohmic contacts give a linear noise power dependence on the sample current 1. We are able to evaluate, therefore, the ohmicity of the electrodes most sensitively from the 1/f noise measurements. Assuming the relevant total electron number between the electrodes, the Hooge parameter is estimated as α H = 5.3 x 10 - 6 at room temperature, in qualitative agreement with the cross correlational 1/f noise model.

−190 dBV2/Hz Preamplifier for Low Frequency Noise Measurements

Low cost highly sensitive preamplifier was made by using the commercially available operational amplifier AD797 which has the input noise equivalent power of −190 dBV2/Hz with 80 dB amplification.

Rhythm Analyses Of Melodies Used To Obtain Women Marathon Gold Medal

In Athena Olympics in 2004 a Japanese girl got the gold medal in Women Marathon games. Just before the beginning, she was listening to some domestic melodies in order to concentrate on the race. The rhythm or power of that music is found to have the typical 1/f noise characteristics. The 1/f music is found effective to concentrate as well as to relax themselves for a fairly long time range, while some short time trial runner uses a kind of white noise like music.