Electrochemically deposited germanium on silicon and its crystallization by rapid melting growth

It is well known that continuous miniaturization of transistors tends to create several problems such as current leakage, short channel effect, etc. Therefore, introduction of new channel material with higher carrier mobilities such as Germanium (Ge) is suggested to overcome this physical limitation and also to improve the performance of conventional transistors in chips. Basically, there are several techniques to grow Ge such as Chemical Vapour Deposition (CVD) and Molecular Beam Epitaxy (MBE) system. However, these processes require high vacuum environment, highly depend on such hard-to-control variables as well as costly. Therefore, an alternative method that practically cheaper to grow Ge utilizing electrochemical and rapid melting technique is investigated here. In this thesis, a systematic study of electrochemical deposition of Ge on Silicon (Si) substrate is outlined. Results show the unwanted Germanium Dioxide (GeO2) tends to form in the air-exposed process and germanium tetrachloride:dipropylene glycol (GeCl4:C6H14O3) electrolyte. Therefore, a Nitrogen (N2) controlled ambient is preferable. The uniform amorphous Ge film on Si (100) substrate was successfully obtained at the optimum current density of 20 mAcm-2 in germanium tetrachloride:propylene glycol (GeCl4:C3H8O2) electrolyte. Crystallization of electrodeposited Ge on Si (100) was demonstrated by rapid melting process. Effect of different annealing temperatures from 1000 to 1100 oC has also been studied. Raman spectra and Electron Backscattering Diffraction (EBSD) result confirmed that the grown Ge was highly oriented with the crystal orientation identical to that of Si (100) substrate at all annealing temperature tested. Based on depth profile from Auger Electron Spectroscopy (AES) measurement and Raman spectra, it was found that Si-Ge mixing occurred upon rapid melting process, particularly at near the Si-Ge interface caused by atoms diffusion. Calculated Si fraction diffused into Ge region in the Si-Ge mixing was high at higher annealing temperature that shows good agreement with solidus curve of Ge-Si equilibrium phase diagram. Correspondingly, the amount of Ge diffused into Si region also increased as annealing temperature increased. The result also shows that the tensile strain turns from high to low with the increase of annealing temperature. In addition, it drastically becomes more compressive as the depth is approaching the interface of Ge and Si. The difference in thermal expansion coefficient is a possible cause to generate such strain behaviour. For applications, the presence of strain in channel will improve the transistor performance by enhancing the carrier mobility. In conclusion, this study proves that electrochemical deposition and rapid melting growth technique are promising methods for synthesizing crystalline Ge and significantly contribute to the improvement of carrier mobility. It is expected that high performance Complementary Metal Oxide Semiconductor (CMOS) transistor scaling and Moore’s Law will continue in the future through new materials introduction in the transistor structure and by incorporating significantly appropriate levels of strain and composition of Ge/Si in the channel

Tracking human movement in office environment using video processing

In this paper, we proposed an approach of multi-person movement tracking in office environment without any identity conflicts. Simple image processing with frame differentiation method is applied to identify multiple human motion. An Expert System is applied to predict next camera occurrence of the tracking human. The main objective of this work is to detect and track multi-human motion using single camera in more than a room in an office

Surface reaction of undoped AlGaN/GaN HEMT based two terminal device in H+ and OH- ion-contained aqueous solution

Gallium nitride is considered as the most promising material for liquid-phase sensor applications due to its chemical stability and high internal piezoelectric polarization. In this work, the sensing responses of undoped-AlGaN/GaN two terminal devices upon exposure to various pH levels in aqueous solution (a mixture of HCl and NaOH) as well as their possible sensing mechanism have been investigated. No reference voltage or gate voltage is applied. The changes in drain-source current, IDS as a function of pH level were evaluated. In the acidic region, there was an almost linear change in IDS where IDS decreased with the increase in pH level. Hence, the translated channel resistance increases with the pH level. High H+ ion concentration at low pH level which corresponds to the large net positive potential on the surface leads to the enhancement of the flow of electrons in 2DEG channel. As the pH level was increased towards neutral point in the acidic region which corresponds to the increase of OH- ion concentration, the net surface potential on the surface starts to be dominated by negative potential. As a result, the 2DEG channel starts to deplete which resulted in the increase of channel resistance. The estimated current and resistance change for sensing area of 1 mm2 and drain-source voltage, VDS of 1- 6 V are in the range of 2.16-80.1 mA/pH and 154.6-500.5 kΩ/pH, respectively. However, the linear decreases of IDS were not continuously observed in the basic region where OH- ions were dominant. The IDS levels were high, showing that the flows of carriers in 2DEG channel were enhanced again. The resistance was low and almost constant in the basic region. It seems to be resulted by the formation of thin Ga(x)O(y) layer on the AlGaN surface contributed by the interaction of OH- with the Ga-face surface. Hence, the net potential on the AlGaN surface seems to be dominated again by the net positive surface potential

Electrochemical deposition of Zinc Oxide thin film using two-terminal setup

This paper reports on deposition process of Zinc Oxide (ZnO) using a simple electrochemical approach. The ZnO thin film was deposited on the Aluminium (Al) substrate in an aqueous solution of Zinc Chloride (ZnCl2) at room temperature using two terminals electrochemical cell that consisted of positive and negative electrodes. Two types of Al substrate were used, which are Al foil and Al plate. Al foil or Al plate acted as the negative electrode (cathode) while Platinum (Pt) wire or Zinc (Zn) plate as the positive electrode (anode). A constant current density of 10 A/m2 was applied in the experiment. 5mM ZnCh and 0.1M potassium chloride (KCl) support solution used as the electrolytic solution. The experiment was carried out by varying the concentration of ZnCl2 electrolyte solution and KCl supporting solution. Three different mixture of electrolyte solution and supporting solution, 125 ml of ZnCl2 + 25 ml of KCl, 100 ml of ZnCl2 + 50 ml KCl and lastly 75 ml ZnCl2 + 75 ml KCl, were used. Each of the samples underwent 30 minutes of deposition process. At the end of the experiment, the morphologies and properties of ZnO were determined by studying the result from Single Electron Microscope (SEM) and Energy Dispersive X-ray spectroscopy (EDX). The structures of the ZnO were found as nanosheet-like network. The results evinced the potential of utilizing simpler setup of electrochemical approach in producing good characteristic of ZnO film for respective applications such as solar cell

Electrical characterization of gold contact on porous silicon layers

Investigation on metallic contact on porous silicon (PS) layers is typically important before final integration into application devices. The electrical characterization of Au thickness of 100 nm and ∼210 nm on ∼3 μm and ∼6 μm PS thickness on PS were studied by measuring the current-voltage (I-V) response. The PS layers of n-type oriented silicon (Si) wafer were prepared by electrochemical etching. Au was deposited on the PS layers using Q150RS automated sputter coater. Based on scanning electron microscope (SEM) images, the thickness of PS was confirmed as 3.07 μm and 6.15 μm for respective samples. The average pore diameter was determined with the aid of ImageJ and Matlab by applying image processing analysis. There were found to be 17.91 μm and 27.26 μm respectively. The I-V curve of PS with Au contact showed significant tendency of Ohmic behaviour compared to non-PS samples that shows Schottky behaviour. The higher conductivity was obtained from sample 3.07 μm of PS thickness with 100 nm Au. Based on this analysis, it can be concluded that thickness of Au and thickness of PS affect the performance of Au-PS device as the conductivity increases as the thickness of Au on PS layers was decreased

Formation of porous silicon: mechanism of macropores formation in n-type si

We report the formation of macropores in n-Si (100) substrates for different etching times of 20, 40 and 60 min at a constant current density of 25 mA/cm2 under front-side illumination in HF:ethanol (1:4) solution. After etching for 20 min, four-branch-shaped pores of various sizes were observed at discrete locations. Etching time of 40 min led to the formation of highly connected four-branch-shaped pores as the branches of adjacent pores appeared to connect to each other. As the etching time was increased further to 60 min, the density of interconnected branches increased remarkably. The macropore formation process occurred in three consecutive phases. The current burst model was used to discuss this process. Formation of four-branch-shaped pores at random locations were observed because current bursts are more likely to nucleate where other current bursts took place initially

Concentration dependence of drift and magnetoresistance ballistic mobility in a scaled-down metal-oxide semiconductor field-effect transistor

The degradation of ballistic mobility in a metal-oxide semiconductor field-effect transistor is attributed to the nonstationary ballistic injection from the contacts as the length of a channel shrinks to the length smaller than the scattering-limited mean free path. Apparent contradiction between the rise of magnetoresistance mobility and fall of drift mobility with increasing channel concentration is attributed to scattering-dependent magnetoresistance factor. The ballistic mean free path of injected carriers is found to be substantially higher than the long-channel drift mean free path. Excellent agreement with the experimental data on length-limited ballistic mobility is obtained

Simple fabrication of an inexpensive impedance based sensor for contamination detection

Escherichia Coli (E-coli) is a bacterium commonly found in the environment, foods and intestines of people and animal. The presence of E-coli in water can severely threaten human health condition. The quality of drinking water is vital and avoid using contaminated water is a must. In fact, the water that contaminated by E-coli is cannot easily be detected by physical observation. Dedicated ways used to detect the presence of E-coli are required. The current techniques available are quite bulky in size, also require high expenses and professional training operation. With these limitation, new technique is proposed which are considerably low-cost and user friendly device in detecting presence of E-coli. The fabrication of impedance based sensor using interdigitated electrode (IDE) and Polydimethylsiloxane (PDMS) as sensor package have been done in this study. The impedance response of the proposed sensor have been observed using impedance analyser. Based on the observation, the sensor device able to differentiate the sample's condition tested in frequency of 1000 Hz until 3000 Hz, but no significant changes observed at the higher frequency range. With the initial results obtained, the proposed device was demonstrated being able to distinguish different E-coli concentration

Stability analysis and vibration control of a class of negative imaginary systems

This paper presents stability analysis and vibration control of a class of negative imaginary systems. A flexible manipulator that moves in a horizontal plane is considered and is modelled using the finite element method. The system with two poles at the origin is shown to possess negative imaginary properties. Subsequently, an integral resonant controller (IRC) which is a strictly negative imaginary controller is designed for the position and vibration control of the system. Using the IRC, the closed-loop system is observed to be internally stable and simuation results show that satisfactory hub angle response is achieved. Furthermore, vibration magnitudes at the resonance modes are suppressed by 48 dB