Arief Udhiarto

Atom devices based on single dopants in silicon nanostructures.

Silicon field-effect transistors have now reached gate lengths of only a few tens of nanometers, containing a countable number of dopants in the channel. Such technological trend brought us to a research stage on devices working with one or a few dopant atoms. In this work, we review our most recent studies on key atom devices with fundamental structures of silicon-on-insulator MOSFETs, such as single-dopant transistors, preliminary memory devices, single-electron turnstile devices and photonic devices, in which electron tunneling mediated by single dopant atoms is the essential transport mechanism. Furthermore, observation of individual dopant potential in the channel by Kelvin probe force microscopy is also presented. These results may pave the way for the development of a new device technology, i.e., single-dopant atom electronics.

Effect of electron injection into phosphorus donors in silicon-on-insulator channel observed by Kelvin probe force microscopy

We have comparatively studied the effects of electron injection in individual phosphorus-donor potential wells at 13 K and 300 K by Kelvin probe force microscopy in silicon-on-insulator metal-oxide-semiconductor field-effect-transistors. As a result, at 13 K, localized single-electron filling into the phosphorus-donor potential well is found, reflecting single-electron tunneling transport through individual donors, whereas at 300 K, spatially extended and continuous electron filling over a number of phosphorus-donors is observed, reflecting drift-diffusion transport.

Photon-Induced Random Telegraph Signal Due to Potential Fluctuation of a Single Donor--Acceptor Pair in Nanoscale Si p--n Junctions

We study the photoresponse of Si nanoscale p–n and p–i–n diodes. As a result, we find a photon-sensitive multilevel random telegraph signal (RTS) in p–n diodes, but not in p–i–n diodes. From this fact and analysis of current jumps in the RTS, the multilevel RTS is ascribed to single photocarrier charging and discharging in a donor–acceptor pair in the depletion region. Thus, it is found that a donor–acceptor pair plays an important role in p–n junctions, while, according to our previous report, a single donor (acceptor) works as an electron (hole) trap in junctionless field-effect transistors.

Trapping of a photoexcited electron by a donor in nanometer-scale phosphorus-doped silicon-on-insulator field-effect transistors

We study interaction of single-electron current and incident photons in nanometer-scale phosphorus-doped silicon-on-insulator field-effect transistors. Trapping events of a photoexcited-electron by a trap donor are observed as random telegraph signals in single-electron-tunneling current flowing through a current-path donor. Trapping causes a potential change at the current-path donor, inducing a current change. An opposite current change is caused by electron detrapping from the trap donor to the current-path donor. This indicates that only a few donors (two donors in this study) work in the interaction between single-electron transport and photoexcited-electron trapping, even in the presence of many donors.

Si-Based Single-Dopant Atom Devices

We have recently proposed and demonstrated a new device concept, “Si-based single-dopant atom device”, consisting of only one or a few dopant atoms in the channel of Si field-effect transistors. The device characteristics are determined by a dopant, which is mediating electron or hole transport between source and drain electrodes. In this paper, our recent results on electronic and photonic applications are introduced. Furthermore, single-dopant images obtained by a scanning probe microscope are also presented.

CO Gas-Induced Resonance Frequency Shift of ZnO-Functionalized Microcantilever in Humid Air

Resonance frequency shift of a zinc oxide- (ZnO-) functionalized microcantilever as a response to carbon monoxide (CO) gas has been investigated. Here, ZnO microrods were grown on the microcantilever surface by a hydrothermal method. The measurement of resonance frequency of the microcantilever vibrations due to the gas was carried out in two conditions, that is, gas flow with and without air pumping into an experiment chamber. The results show that the resonance frequency of the ZnO-functionalized microcantilever decreases because of CO in air pumping condition, while it increases when CO is introduced without air pumping. Such change in the resonance frequency is influenced by water vapor condition, and a possible model based on water-CO combination was proposed.

Effect of anode and cathode workfunction on the operating voltage and luminance of a single emissive layer organic light emitting diode

Organic light emitting diodes (OLED) are considered to be a promising candidate for light sources as well as for flat panel display because of their numerous advantageous. Two important parameters of an OLED among many other parameters to measure OLED performance are operating voltage and luminance. Those two parameters are believed to be strongly influenced by an anode and cathode workfunction of materials used as electrodes. In this paper, we study the effect of anode and cathode workfunction on the operating voltage and luminance of a single emissive layer organic light emitting diode. Devices with five different cathodes: Aluminum (Al), Calcium (Ca), Magnesium (Mg), Argentum (Ar), and Cuprum (Cu) and three different anodes: Indium Thin Oxide (ITO), Poly-(3,4-Ethylenedioxidythiophene)-Poly (Styrene Sulfonate) (PEDOT:PSS), Zinc Oxide (ZnO) are compared and analyzed. A 2 nm thick of Polyfluorene (PFO) is used as an emissive layer. SimOLED is used to simulate and analyze both electrical and optical characteristics. Current voltage luminance (IVL) characteristics are simulated under forward biased from 0 to 10 V. We found that the use of anode with higher workfunction can reduce operating voltage as well as increases device luminance. On the other hand, the use of lower workfunction of cathode can reduce operating voltage however it is not always increasing device luminance. The decrease of the operating voltage by increasing anode workfunction and decreasing cathode workfunction are ascribed to the barrier lowering of the holes and the electrons respectively.

The performance of Si/sub 0.2/Ge/sub 0.8//Si solar cell

Solar cell is optimized to convert solar radiation to electrical current with conversion efficiency as high as possible. Due to their superior performance compared to conventional silicon devices we used the Si/sub x/Ge/sub 1-x/ strained layer for increasing the efficiency of solar cell device. By using simulations tools, i.e. pc1d version 5.6, we investigate and analysis the performance of Si/sub 0.2/Ge/sub 0.8//Si solar cell, especially open circuit voltage, short circuit current, fill factor which will affect the efficiency of the device. We also compare it with conventional silicon solar cell in order to examine their performances and the thickness of both device structures. The Si/sub x/Ge/sub 1-x/ strained layer we applied contents 80% germanium. Results show that by inserting Si/sub 0.2/Ge/sub 0.8/ strained layer in device structure open circuit voltage and short circuit current has been optimal and the thickness of the device compared to conventional silicon solar cell is 1/17 times.