T. C. Huang

EFFECTS OF COLUMN-III ALKYL SOURCES ON DEEP LEVELS IN GAN GROWN BY ORGANOMETALLIC VAPOR-PHASE EPITAXY

Two different kinds of n‐type GaN films were prepared by organometallic vapor phase epitaxy, one by using trimethylgallium (TMGa) and another by using triethylgallium (TEGa) as the alkyl source. Schottky diodes with well‐behaved current–voltage and capacitance–voltage characteristics were fabricated. Deep‐level transient spectroscopy studies were performed on these samples. Three distinct deep levels, labeled E1, E2, and E3, were measured in the film grown with TMGa, with an activation energy of 0.14, 0.49, and 1.63±0.3 eV, respectively. Only one level, E3, was observed in the film prepared with TEGa.

Determination of built-in field by applying fast Fourier transform to the photoreflectance of surface-intrinsic n+-type doped GaAs

Photoreflectance spectroscopy of surface-intrinsic n+-doped (s-i-n+) GaAs has been measured at various power densities (Ppu) of a pump beam. Many Franz–Keldysh oscillations (FKOs) were observed above the band-gap energy, which will enable the electric-field strength (F) to be determined from the periods of the FKOs. Field F thus obtained is subject to photovoltaic effects. In order to reduce the photovoltaic effects from the pump beam, Ppu was kept below 10 μW/cm2 in the previous experiments. Here, we demonstrate that the built-in field can be determined at a larger Ppu by using fast Fourier transform techniques.

Broadly tunable self-starting passively mode-locked Ti:sapphire laser with triple strained-quantum-Well saturable Bragg Reflector

Abstract We demonstrate broadband mode-locking of femtosecond Ti:sapphire lasers with a new type of saturable Bragg reflector (SBR). Triple-strained quantum wells with separate and sequential bandgaps were used as the absorbing layer. The saturation fluence was as low as 7 μJ/cm 2 . Self-starting sub-100 fs pulses tunable from 768 to 804 nm were generated in a standard X-folded cavity without intracavity tight focusing on the SBR or temperature tuning. The threshold fluence for self-starting mode-locking was 1 μJ/cm 2 .

Junction-less poly-Ge FinFET and charge-trap NVM fabricated by laser-enabled low thermal budget processes

A doping-free poly-Ge film as channel material was implemented by CVD-deposited nano-crystalline Ge and visible-light laser crystallization, which behaves as a p-type semiconductor, exhibiting holes concentration of 1.8u2009×u20091018u2009cm−3 and high crystallinity (Raman FWHM ∼ 4.54u2009cm−1). The fabricated junctionless 7u2009nm-poly-Ge FinFET performs at an Ion/Ioff ratio over 105 and drain-induced barrier lowering of 168u2009mV/V. Moreover, the fast programming speed of 100 μs–1u2009ms and reliable retention can be obtained from the junctionless poly-Ge nonvolatile-memory. Such junctionless poly-Ge devices with low thermal budget are compatible with the conventional CMOS technology and are favorable for 3D sequential-layer integration and flexible electronics.

Critical point energy as a function of electric field determined by electroreflectance of surface-intrinsic-n+ type doped GaAs

Electroreflectance of surface-intrinsic-n+ type doped GaAs has been measured over a various biased voltage. The spectra have exhibited many Franz–Keldysh oscillations (FKOs) above band gap energy Eg. The electric field F and critical point energy Ec can be determined from the slope and intercept of FKOs fitting. Hence, we can obtain Ec as a function of F. In most of previous works, Ec is taken as Eg. However, it was found that Ec increases with F in this work. In order to explain this, the gain of energy of electron and hole in F was discussed.

Enabling n-type polycrystalline Ge junctionless FinFET of low thermal budget by in situ doping of channel and visible pulsed laser annealing

A low-thermal-budget n-type polycrystalline Ge (poly-Ge) channel that was prepared by plasma in-situ-doped nanocrystalline Ge (nc-Ge) and visible pulsed laser annealing exhibits a high electrically active concentration of 2 × 1019 cm−3 and a narrow Raman FWHM of 3.9 cm−1. Furthermore, the fabricated n-type poly-Ge junctionless FinFET (JL-FinFET) shows an I on/I off ratio of 6 × 104, V th of −0.3 V, and a subthreshold swing of 237 mV/dec at V d of 1 V and DIBL of 101 mV/V. The poly-Ge JL-FinFET with a high-aspect-ratio fin channel is less sensitive to V th roll-off and subthreshold-swing degradation as the gate length is scaled down to 50 nm. This low-thermal-budget JL-FinFET can be integrated into three-dimensional sequential-layer integration and flexible electronics.

The effects of the magnitude of the modulation field on electroreflectance spectroscopy of undoped-n+ type doped GaAs

The electroreflectance (ER) spectra of an undoped-n+ type doped GaAs has been measured at various amplitudes of modulating fields (δF). Many Franz–Keldysh oscillations were observed above the band gap energy, thus enabling the electric field (F) in the undoped layer to be determined. The F is obtained by applying fast Fourier transformation to the ER spectra. When δF is small, the power spectrum can be clearly resolved into two peaks, which corresponds to heavy- and light-hole transitions. When δF is less than ∼1/8 of the built-in field (Fbi∼77u2009420u2009V/cm), the F deduced from the ER is almost independent of δF. However, when larger than this, F is increased with δF. Also, when δF is increased to larger than ∼1/8 of Fbi, a shoulder appears on the right side of the heavy-hole peak of the power spectrum. The separation between the main peak and the shoulder of the heavy-hole peak becomes wider as δF becomes larger.

Temperature dependence of Fermi level obtained by electroreflectance spectroscopy of undoped n+-type doped GaAs

The electroreflectance (ER) spectra of an undoped n+-type doped GaAs have been measured over a range of temperature from 25 to 400 K. Many Franz–Keldysh oscillations were observed above the band-gap energy, which enabled the electric field strength and, hence, also the Fermi level to be determined. The photovoltaic effect is shown to be negligible, even at the low temperature. The experiment shows that the Fermi level decreases with increasing temperature and has almost the same temperature dependence as the energy gap. It is pinned at about 0.63 of energy gap below the conduction band.

Electroreflectance of surface-intrinsic- n + -type-doped GaAs by using a large modulating field

It is known that electroreflectance of surface-intrinsic-n+-type-doped GaAs has exhibited many Franz–Keldysh oscillations to enable the application of fast Fourier transform to separate the heavy- and light-hole transitions. However, each peak still contains two components, which belong to F+δF/2 and F−δF/2, respectively, where F is the electric-field strength in the undoped layer and δF is the modulating field of applied ac voltage (Vac). In order to resolve the heavy- and light-hole transitions, δF was kept much smaller than F in the previous works. In this work, we have used a larger Vac and, hence, a larger δF, to further separate the peaks. The peaks can be divided into two groups which belong to F+δF/2 and F−δF/2, respectively. The peak belonging to the heavy-hole transition and F−δF/2 can be singled out to compare with the Airy function theory.

Effects of polarization on electroreflectance spectroscopy of surface-intrinsic n+-type doped GaAs

The electroreflectance (ER) spectra of a surface-intrinsic n+-type doped (100) GaAs have been measured at various polarization angles of the probe beam. Several Franz–Keldysh oscillations were observed above the band-gap energy, thus enabling heavy- and light-hole transitions to be separated by the application of the fast Fourier transform to the ER spectra. From this, the ratios of the amplitudes of the light- to heavy-hole transitions versus angle of polarization were obtained. At a large incident angle (80°), the strength of the field of the probe beam in the normal direction of the sample (Fz) was varied from zero to a larger component. It was found that the ratios increased with increasing Fz which is consistent with the theory that the light-hole transition becomes more enhanced with z-polarized light.