T. W. Kim

Structural properties of BaTiO3 thin films on Si grown by metalorganic chemical vapor deposition

Ferroelectric BaTiO3 thin films were grown on Si(100) substrates at a temperature of 600u2009°C by in situ metalorganic chemical vapor deposition. X‐ray diffraction and transmission electron microscopy results suggested that the 〈110〉 direction of the BaTiO3 preferred oriented films is parallel with the (100) direction of the Si substrates. Auger electron spectroscopy measurements showed that the compositions of the as‐grown films were with a uniform distribution throughout the thickness of the films and with a sharp interface. These results indicate that the failure to obtain BaTiO3 epitaxial films was due to the formation of an interfacial amorphous layer prior to the creation of the films.

Structural and electrical properties of Al2O3 thin films on p-Si grown by low-pressure metalorganic chemical vapor deposition

Abstract Al2O3 films were grown by metalorganic chemical vapor deposition on p-Si(100) orientation substrates using Al(OC3H7)3 and N2O via pyrolysis. Raman spectroscopy showed the optical phonon modes of the Al2O3/Si structure. The stoichiometry of the Al2O3 film was observed by Auger electron spectroscopy. Capacitance-voltage measurements clearly showed metal-insulator-semiconductor behaviors for the Al/Al2O3/Si diodes with the Al2O3 insulator gate, and the interface state densities at the Al2O3/Si interface were approximately 1011 eV cm-2 at the middle of the Si energy gap. These results indicate that Al2O3 films on Si have potential applications as insulator films.

The interfacial layer formation of the Al2O3/Si structures grown by low‐pressure metalorganic chemical vapor deposition

Metalorganic chemical vapor deposition of Al2O3 using Al(O‐C3H7)3 and N2O via pyrolysis was investigated with the goal of producing Al2O3 epitaxial films on p‐Si (100) substrates. Room‐temperature capacitance‐voltage measurements clearly showed metal‐insulator‐semiconductor behaviors for the samples with the Al2O3 insulator gate, and the interface state densities at the Al2O3/p‐Si interface were approximately 1011 eV−1u2009cm−2 at the middle of the Si energy gap. Auger depth profiles demonstrated that the Al2O3/Si interface was not abrupt, and transmission electron microscopy verified the formation of an interfacial layer in the Al2O3/Si interface and the formation of a polycrystalline Al2O3 thin film. These results indicated that the failure to form Al2O3 epitaxial films was due to the formation of an interfacial layer prior to the growth of the Al2O3 layer.

Growth and characterization of Al2O3 insulator gate on p-InP and p-Si by metallorganic chemical vapour deposition at low temperatures

Metallorganic chemical vapour deposition of Al2O3 from Al(O-C3H7)3 via pyrolysis at low (∼280 °C) temperature was investigated with the goal of producing high quality Al2O3/p-InP (1 0 0) and Al2O3/p-Si (1 0 0) interfaces. Ellipsometer measurements of Al2O3 have determined the refractive index of the film to be about 1.55. Room temperature capacitance-voltage measurements were used to characterize the electrical properties of the structures after metal gate electrodes have been deposited. Low temperature conductance-voltage measurements were also carried out to investigate the quality of the Al2O3/InP interfaces. The interface state densities Al2O3/p-InP and Al2O3/p-Si determined from deep-level transient spectroscopy were approximately 1012 eV−1 cm−2 and 1011 eV−1 cm−2.

Electronic parameters of the two-dimensional electron gas in modulation- doped single quantum wells due to an embedded deep step layer

The Shubnikov–de Haas (S–dH) measurements at 1.5 K clearly demonstrated the existence of a two-dimensional electron gas (2DEG) in the modulation-doped Al0.25Ga0.75As/InyGa1−yAs/GaAs single and step quantum wells, and the fast Fourier transformation results for the S–dH data clearly indicated the electron occupation of one subband in the asymmetric single and step quantum wells. While the electron carrier density of the 2DEG in the step quantum well was larger than that in the single quantum well due to the larger conduction-band discontinuities, the mobility of the 2DEG in the step quantum well was smaller than that in the single quantum well because of the interface scattering resulting from the embedded step well. The electron effective mass in the step quantum well was smaller than that in the single quantum well, which was consistent with a smaller mass of the embedded deep step layer. The electronic subband energy, the energy wave function, and the Fermi energy in the InyGa1−yAs step quantum wells we...

Electronic property variations due to an embedded potential barrier layer in modulation-doped step quantum wells

Electronic property variations of a two-dimensional electron gas (2DEG) in modulation-doped step quantum wells due to an embedded potential barrier were studied by performing Shubnikov–de Haas (SdH), Van der Pauw–Hall-effect, and cyclotron resonance measurements on two kinds of InxGa1−xAs/InyAl1−yAs step quantum wells which were one without and the other with an embedded barrier. The fast Fourier transformation results for the SdH data at 1.5 K indicated the electron occupation of two subbands in both step quantum wells. The total electron carrier density and the mobility of the 2DEG in the step quantum well with an embedded barrier were smaller than those in the quantum well without an embedded barrier. The electron effective masses were determined from the slopes of the main peak absorption energies as functions of the magnetic field, and satisfied qualitatively the nonparabolicity effects in both quantum wells. The electronic subband energies, the wave functions, and the Fermi energies were calculated ...

Thermally stimulated current of amorphous selenium

Deep trap properties such as activation energy, capture cross section, and polarity in the amorphous selenium bulk are investigated using a thermally stimulated current (TSC). Two peaks are found near 220 and 330 K in the TSC curve, and the activation energies corresponding to these two peaks are distributed from 0.20 to 0.22 eV and from 1.04 to 1.10 eV. It is found that the trapped carriers near the temperature 220 K are mainly holes.

Thermally stimulated current of Li+ ion‐implanted amorphous selenium

A thermally stimulated current (TSC) technique is applied to examine the activation energy, capture cross sections, escape frequency, and trap polarity in amorphous Se (a‐Se) implanted with low energy (<20 keV) Li+ ions. TSC glow curves for Li+ ‐ion‐implanted a‐Se show two peaks near 230 and 330 K. The value of δ/ω is 0.46 for 230 K, which means that the thermally stimulated currents are due to the first‐order kinetics. The trap activation energy levels obtained by peak shape method and various heating rate methods are distributed from 0.22 to 0.33 eV for the 230‐K peak and to 1.42 eV for the 330‐K peak. The values of the capture cross section and the escape frequencies are 2.75×10−19 cm2 and 5.5×105 s−1 for the 230‐K peak, and 5.75×10−20 cm2 and 6.43×105 s−1 for the 330‐K peak, respectively. It is found that the trapped charge carriers are mainly holes in Li+ ion‐implanted a‐Se.

Angular distributions of current density in liquid Ga‐ion sources

Current‐voltage (I‐V) characteristics and angular distribution of the current density of a liquid gallium ion source were investigated under various emitting tip temperatures and surface flow impedances. It is shown that the I‐V slope is significantly influenced by the flow impedance of the liquid gallium on the emitting tip. The slopes of the I‐V curve are shown to be steep for an emitting tip with a rough surface, and gentle for a smooth surface. The angular distribution of Ga ions was determined by measuring the current on metal rings concentric with the emission axis and located so as to form a portion of a hemisphere. The current density was found to be depressed near the center compared to the surrounding region. This density distribution persists for various axial locations of the rings. Moreover, the angular profile of current density at fixed axial locations is found to be identical for the same amount of emission current, irrespective of the tip‐surface condition or the applied voltage. It shows...

Effects of electric fields on the silver photodoping of As2Se3 films

The effects of different electric fields (4.2, 8.3, 12.5, 16.7 and 20.8 Vcm−1) on the sheet resistance, Rs, and optical band gap, Eobg, of As2Se3 samples (1×105nm) that were photodoped by Ag (5×103nm) have been studied. The Rs and Eobg of samples subjected to an electric field of 12.5 Vcm−1 decrease linearly to a distance of 5 mm from both electrodes, and then saturate at larger distances. This result suggests that there is a critical value of the electric field which affects photodoping. The dependence of Rs and Eobg on the distance from the electrodes shows similar profiles for these electrodes.