Chih-Hao Tsai

Nanogap formation by palladium hydrogenation for surface conduction electron emitters fabrication

Nanometer-scale gaps in Pd strips are obtained by hydrogen absorption under high pressure treatment. The resulting lattice constant increase due to the Pd phase transformation after hydrogen uptake results in a large compressive stress on the thin Pd films. Under proper geometric arrangement of the Pd electrode within a surface conduction electron (SCE) emitter structure, a single nanogap per SCE device is obtained. A turn-on voltage of 41V is observed for emitters with a 25nm gap.

ENHANCEMENT OF ELECTRON-WAVE REFLECTION BY SUPERLATTICES WITH MULTIPLE STACKS OF MULTIQUANTUM BARRIERS

We report a superlattice (SL) with multiple stacks of multiquantum barriers (MQB), which can reflect electrons more effectively than with a single stack of MQB. The reflectivities are calculated and compared with one another for a variety of potential barrier structures. The multistack SL has a wider energy spectrum within which electrons are reflected. Four types of n‐GaAs/i‐barrier/n‐GaAs diodes were fabricated to confirm the calculated results. The current‐voltage characteristics measured at 77 K for these diodes show that the turn‐on voltage increases with the number of stacks of MQBs in the SL. This is in agreement with our calculated results.

Field-emission properties of novel palladium nanogaps for surface conduction electron-emitters

We explore novel nanometer-scale gaps with different widths in palladium (Pd) thin-film strips using hydrogen absorption under high-pressure conditions and different temperatures. Both the experimental measurement and numerical calculation are conducted to examine the electron conduction properties of the newly proposed surface conduction electron-emitters (SCEs). It is shown that this novel structure exhibits a high emission efficiency, so that a low turn-on voltage of 40 V for an SCE with a 30 nm nanogap is obtained. A calibrated model is adopted to predict the effects of the emitter thickness and different material work functions on emission current with different width of nanogaps. It is found that the heightened thickness increases the emission current. However, it tends to saturate for smaller nanogaps. The decrement of work function is proportional to the increase in emission current, which is independent of the width of nanogap.

Effect of Process Variation on Field Emission Characteristics in Surface-Conduction Electron Emitters

In this paper, we explore the effect of process variation on field emission characteristics in surface-conduction electron emitters. The structure of Pd thin-film emitter is fabricated on the substrate and the nanometer scale gap is formed by the focused ion beam technique. Different shapes of nanogaps due to the process variations are investigated by the experiment and three-dimensional Maxwell particle-in-cell simulation. Four deformation structures are examined, and it is found that the type 1 exhibits high emission efficiency due to a stronger electric field around the apex and larger emission current among structures. The electron emission current is dependent upon the angle of inclination of surface. Hydrogen plasma treatment is also used to increase the edge roughness of the nanogap and thereby dramatically improve the field emission characteristics. For the nanogap with a separation of 90 nm, the turn-on voltage significantly reduces from 60 to 20 V after the hydrogen plasma treatment.

Thermal annealing of Pd/InAlAs Schottky contacts for transistor buried-gate technologies

We studied the thermal reaction of Pd/In0.52Al0.48As contacts using capacitance–voltage (C–V), current–voltage, Auger electron spectroscopy, and x-ray diffraction analyses and compared the results to those for Pd/Al0.25Ga0.75As and Pd/In0.53Ga0.47As contacts. The thickness of InAlAs consumed by the reaction during annealing was calculated directly from the measured C–V profiles. Pd starts to react with InAlAs at a temperature of 100 °C, lower than it does with AlGaAs. For thermally annealed Pd/InAlAs and Pd/AlGaAs, both compositional and structural changes were found at the Pd/semiconductor interface. However, in heat-treated Pd/InGaAs samples, compositional changes but no structural changes were observed.

Direct observation of Si delta‐doped GaAs by transmission electron microscopy

Direct observation of the Si delta‐doped layer in GaAs has been achieved by high resolution transmission electron microscopy. Samples with different Si doses, from half a monolayer to two monolayers, were studied. The observed spreading of the delta‐doped layer showed that Si atoms are largely confined in five monolayers at most (in the highest dose case), indicating excellent confinements of dopants in GaAs. From the images, the Si atoms were uniformly distributed in the doped layer, no cluster formation was observed. For delta‐doped GaAs grown at low temperature (480 °C), stacking faults originated from the doped layers were observed. These faults were thought to be caused by the large unrelaxed strain in the low‐temperature grown GaAs.

A simple method to characterize the afterpulsing effect in single photon avalanche photodiode

A simple method is introduced for studying the afterpulsing effect in InGaAs single photon avalanche photodiode. The afterpulsing probability is obtained through measuring the detection efficiencies of various biasing pulses, while the incident photons are kept constant. The effect of excess bias and temperature on the afterpulsing probability is investigated. When the device temperature is higher than 170 K, the afterpulsing probability is lower than 5% for all excess bias voltages because the trapped carrier lifetime is much shorter than the repetition period.

INFLUENCE OF X-VALLEY SUPERLATTICE ON ELECTRON BLOCKING BY MULTIQUANTUM BARRIERS

Four n‐i‐n GaAs/AlGaAs diodes have been used to demonstrate that at room temperature the carrier blocking is influenced by the X‐valley superlattice in a multiquantum barrier. The diode with a Γ‐X crossover multiquantum barrier has a current at least three orders lower than the corresponding diode with only a bulk barrier. However, diodes without Γ‐X crossover barriers have resistance as low as 10 Ω in spite of whether a multiquantum barrier exists or not. This indicates that the X‐valley superlattice plays an important role in blocking the current flowing across/through a multiquantum barrier.

P‐101: Nanogap Fabrication on Palladium Electrodes for Field Emission Display Applications

We have used focused ion beam (FIB) to produce nanogaps on palladium thin film line electrodes. The two facing cross-sections of the as-prepared nanogap were smooth and exhibited a large turn-on voltage for electron field emission depending on the separation of the gap. Hydrogen plasma treatment was used to increase the edge roughness of the nanogap, and thereby dramatically improve the field emission characteristics. for a gap with a separation of 90 nm, the turn-on voltage reduced to 50 V from 175 V after the hydrogen plasma treatment.

P-102: Three-Dimensional Simulation of Novel Surface Conduction Electron-Emitters

We for the first time explore a novel structure of Pd thin-film emitter fabricated on the substrate with various gaps ranging from 30 nm to 90 nm. with the 3D electromagnetic particle-in-cell (PIC) simulation, we study the conducting mechanism and driving current for the new device with one palladium field emission emitter. Compared with the experimental data, our calibrated simulation predicts a high emission efficiency of the investigated device structure. It is found that the turn-on voltage is about 50V and a very high electron emission current of 0.1 mA is estimated at the anode voltage of 80 V for one emitter. The novel structure of surface conduction electron-emitter (SCE) has the advantages of the simple fabrication and the high emission efficiency. Based upon the numerical procedure, we are currently investigating the emission efficiency for more advanced structures of SCE.