Measurement of reduction in SHG coefficient of LiNbO/sub 3/ by proton exchanging

The SHG coefficient of a proton-exchanged layer of LiNbO/sub 3/, relative to the bulk value, has been measured for the first time by non-phase-matched SHG using a grating sample. It was found that the d/sub 33/ coefficient is reduced to approximately 0.5 of the bulk value by proton exchanging in pure benzoic acid.<>     

Proton-exchanged optical waveguides in LiNbO/sub 3/ using octanoic acid

Low-loss proton-exchanged planar waveguides in z-cut LiNbO/sub 3/ were fabricated and characterized optically using octanoic acid as a proton source. The waveguide exhibited a step-index profile with an index change of 0.118 measured at 0.633 mu m. The lowest waveguide propagation loss measured was 1.2 dB/cm, and it was reduced further to 0.4 dB/cm after annealing. The diffusion rate and the activation energy using this acid were found to be lower than those reported using other acids.<>     

A novel wet-etching method using electric-field-assisted proton exchange in LiNbO/sub 3/

This paper presents a novel wet etching method for LiNbO/sub 3/ using electric-field-assisted proton exchange. By applying voltage with appropriate polarity on designed electrodes placed on both sides of substrate, the induced electric-field distribution can effectively suppress or enhance proton diffusion in the lateral and depth directions. Thus, the proton-exchanged range in LiNbO/sub 3/ can be expertly manipulated. Because the proton-exchanged region can be removed by using a mixture of HF/HNO/sub 3/ acids, the proposed wet-etching method can effectively control the shape of the etched region in the LiNbO/sub 3/ substrate. Under appropriate electrode and proton-exchange parameters, a vertical sidewall with smooth surface is successfully produced, which makes fabricating reflection mirrors and T-junctions in LiNbO/sub 3/ possible. By utilizing the proposed wet-etching method, optical integrated circuits with higher integration density can be fabricated in LiNbO/sub 3/.     

Recovery of second-order optical nonlinearity in annealedproton-exchanged LiNbOx

The second-order nonlinear coefficients measured in proton-exchanged LiNbO₃ as a function of annealing time are discussed. Measurements of reflected second-harmonic power indicate that the second-order nonlinear coefficient d₃₃ is reduced to 60% of the bulk value as a result of proton exchange in pure benzoic acid. It is also shown that annealing restores the d-coefficients to almost the original value of the virgin crystal. For example, recovery to ~90% of the bulk value was obtained for a sample with a 0.3-μm-bulk proton-exchanged layer, annealed for 10 h at 350°C     

Optical gain in proton-exchanged Cr:LiNbO/sub 3/ waveguides

The authors report on a study of optical gain in chromium-doped LiNbO/sub 3/ waveguides formed by the proton-exchange process. Optical gain in proton-exchanged Cr:LiNbO/sub 3/ channel waveguides has been measured for the first time. These waveguides show potential for diode-laser pumping of an integrated, broadband tunable laser in the 750-1150 nm spectral range.<>     

Electrooptically wavelength-tunable polarization converter utilizing strain-optic effect on X-cut LiNbO/sub 3/

A new electrooptically wavelength-tunable polarization converter by strain-optic effect on LiNbO/sub 3/ is presented. The polarization conversion is achieved by the tilt of waveguide principal axis caused by the stress induced by the proton-exchanged region on the single side of the waveguide. Simply increasing the proton-exchange time can enlarge the stress-distributed region and its interaction with the input light, thus, the conversion efficiency can be enhanced. By electrooptic effect, the wavelength of maximum conversion can be tuned at a rate of 0.081 nm/V with a maximum conversion efficiency of 92.4%.     

Direct comparison of hydrogen depth distributions and refractive index profiles in annealed proton-exchanged Z-cut LiNbO/sub 3/ waveguides

For the first time, to the authors' knowledge, hydrogen distributions in weakly and strongly annealed proton-exchanged z-cut LiNbO/sub 3/ have been measured using modified secondary ion mass spectrometry and correlated with refractive index profiles determined by optical waveguide measurements.<>     

Index profile of proton-exchanged waveguides in LiNbO/sub 3/ using pyrophosphoric acid

A systematic study was carried out on proton-exchanged LiNbO/sub 3/ optical waveguides using pyrophosphoric acid. A maximum surface index increase of 0.145 was measured at 0.633 mu m for z-cut substrates. The index profile could be accurately modelled by a polynomial expression of simply by a 'truncated' step-index profile.<>     

Proton-exchanged LiNbO3 waveguides: the effects ofpost-exchange annealing and buffered melts as determined by infraredspectroscopy, optical waveguide measurements, and hydrogen isotopicexchange reactions

Infrared spectroscopy in the OH stretching region has been used to determine the extent of proton exchange in x- and z-cut lithium niobate as a function of temperature and time. The behavior observed is consistent with the occurrence of a diffusion-limited process within LiNbO₃. Apparent activation energies for the process determined from infrared spectroscopic measurements are consistent with the existence of a minimum exchange temperature and show that a relationship exists between waveguide depth and absorption band area. The measurements are also shown that hydrogen-bonded OH is substantially removed by annealing and that the extent of its formation is reduced by using buffered (lithium benzoate/benzoic acid) melts. It is suggested that hydrogen-bonded OH groups are responsible for many of the problems associated with proton-exchanged waveguides. Therefore, implementation of either annealing or buffered melts as part of the fabrication process is required to realize good-quality proton-exchanged waveguides     

Improvement of electrical and reliability properties of tantalum pentoxide by high-density plasma (HDP) annealing in N/sub 2/O

This study aims to improve the electrical characteristics and reliability of low-pressure chemical vapor deposited (LPCVD) tantalum pentoxide (Ta/sub 2/O/sub 5/) films by a new post-deposition annealing technique using high-density plasma (HDP). Experimental results indicate that excited oxygen atoms generated by N/sub 2/O decomposition from HDP annealing can effectively reduce the carbon and hydrogen impurity concentrations and repair the oxygen vacancies in the as-deposited CVD Ta/sub 2/O/sub 5/ film, thereby resulting in a remarkable reduction of the film's leakage current. Two other post-deposition annealing conditions are compared: HDP O/sub 2/ annealing and conventional plasma O/sub 2/ annealing. The comparison reveals that HDP N/sub 2/O annealing has the lowest leakage current and superior time-dependent dielectric breakdown (TDDB) reliability.     

New method of domain inversion in LiNbO/sub 3/ using thermal oxidation of Ti film

A new technique for fabricating domain inversion regions in -c face LiNbO/sub 3/ by thermal oxidation of Ti is reported. This technique can minimise refractive index changes in such regions, thus it is suitable for quasiphase-matching (QPM) second harmonic generation (SHG). A prototype QPM waveguide SHG device is also demonstrated.<>     

LiNbO/sub 3/ waveguide SHG device with ferroelectric-domain-inverted grating formed by electron-beam scanning

A ferroelectric-domain-inverted grating was fabricated by electron beam scanning in LiNbO/sub 3/. A waveguide second harmonic generation (SHG) device with the grating was fabricated and demonstrated for the first time. The experiments were performed using a CW-Nd:YAG laser, and normalised SHG conversion efficiency of 50%/W was obtained.<>     

Cherenkov second-harmonic generation in multilayer waveguidestructures

A model is presented that calculates the features of Cerenkov second-harmonic generation (SHG) in planar dielectric waveguides with an arbitrary index profile. These waveguides are represented by a stack of homogeneous layers of biaxially birefringent media. The model describes type I SHG in channel waveguides within a few approximations, such as the assumption of a quasi-slab channel geometry. Furthermore, this study comprises results of previous step-index models given in the literature, as a particular case of a one-layer structure. These results are in close agreement with measurements of the SHG efficiency in Rb-exchanged erfc waveguides in KTP materials, and in proton-exchanged step waveguides in LiNbO₃ as functions of the pump wavelength     

Anomalous refractive index change in proton exchanged LiNbO3 waveguides after annealing

An anomalous refractive index change in proton-exchanged LiNbO₃ optical waveguides formed at the benzoic acid melt after annealing has been observed and explained     

Bias-temperature instabilities of polysilicon gate HfO/sub 2/ MOSFETs

Bias-temperature instabilities (BTI) of HfO/sub 2/ metal oxide semiconductor field effect transistors (MOSFETs) have been systematically studied for the first time. NMOS positive BTI (PBTI) exhibited a more significant V/sub t/ instability than that of PMOS negative BTI (NBTI), and limited the lifetime of HfO/sub 2/ MOSFETs. Although high-temperature forming gas annealing (HT-FGA) improved the interface quality by passivating the interfacial states with hydrogen, BTI behaviors were not strongly affected by the technique. Charge pumping measurements were extensively used to investigate the nature of the BTI degradation, and it was found that V/sub t/ degradation of NMOS PBTI was primarily caused by charge trapping in bulk HfO/sub 2/ rather than interfacial degradation. Deuterium (D/sub 2/) annealing was found to be an excellent technique to improve BTI immunity as well as to enhance the mobility of HfO/sub 2/ MOSFETs.     

Effects of H/sub 2/ annealing and polysilicon emitter structure on H/sub FE/ of n-p-n bipolar junction transistors

This paper presents the effects of H/sub 2/ annealing and polysilicon emitter structures on H/sub FE/ characteristics of n-p-n bipolar junction transistors. The increase of the number of H/sub 2/ annealing steps results in the device performance (H/sub FE//spl times/V/sub A/) improvement by 27.8%, due to the formation of H-Si dangling bonds, which allow the decrease of the base current. In addition, the bilayer of undoped polysilicon deposition/ion implantation and in situ doped polysilicon in the ploy emitters greatly improve the level of H/sub FE/ reliability and 1/f noise characteristic. The experimental results of H-Si dangling bond property at the polysilicon grain boundaries and polysilicon interface with the H/sub 2/ annealing steps in n-p-n bipolar junction transistor formulation will be also presented.     

Improving the electrical integrity of Cu-CoSi/sub 2/ contacted n/sup +/p junction diodes using nitrogen-incorporated Ta films as a diffusion barrier

The study on improving the electrical integrity of Cu-CoSi/sub 2/ contacted-junction diodes by using the reactively sputtered TaN/sub x/ as a diffusion barrier is presented in this paper. In this study, the Cu (300 nm)-CoSi/sub 2/ (50 nm)/n/sup +/p junction diodes were intact with respect to metallurgical reaction up to a 350/spl deg/C thermal annealing while the electrical characteristics started to degrade after annealing at 300/spl deg/C in N/sub 2/ ambient for 30 min. With the addition of a 50-nm-thick TaN/sub x/ diffusion barrier between Cu and CoSi/sub 2/, the junction diodes were able to sustain annealing up to 600/spl deg/C without losing the basic integrity of the device characteristics, and no metallurgical reaction could be observed even after a 750/spl deg/C annealing in a furnace. In addition, the structure of TaN/sub x/ layers deposited on CoSi/sub 2/ at various nitrogen flow rates has been investigated. The TaN/sub x/ film with small grain sizes deposited at nitrogen flow ratios exceeding 10% shows better barrier capability against Cu diffusion than the others.     

GaN MOS device using SiO/sub 2/-Ga/sub 2/O/sub 3/ insulator grown by photoelectrochemical oxidation method

We report on a SiO/sub 2/-Ga/sub 2/O/sub 3/ gate insulator stack directly grown on n-type GaN by the photoelectrochemical oxidation method. The resultant MOS devices are fabricated using standard photolithography and liftoff techniques. The effect of annealing temperature on the SiO/sub 2/-Ga/sub 2/O/sub 3//n-type GaN MOS devices is investigated. The properties of high breakdown field, low gate leakage current, and low interface state density are investigated for the MOS devices.     

Optical activity induced in Bi/sub 4/Ge/sub 3/O/sub 12/ waveguides by ion implantation

The authors report data for ion implanted Bi/sub 4/Ge/sub 3/O/sub 12/ in which the modified material becomes optically active. The optical rotary power, after implantation and annealing, increases from zero to some 90 degrees /mm. The effect is attributed to an ion beam induced relaxation to a modified BiGeO phase.<>     

Second-harmonic generation in ion-implanted KTiOPO/sub 4/ planar waveguides

The first example of second harmonic generation (SHG) in an ion implanted KTiOPO/sub 4/ waveguide is reported. This was formed by helium implantation, and SHG was achieved using zero order mode phase matching at lambda approximately=1.07 mu m. The results indicate that the high nonlinearity remains in the guiding region after implantation. The conversion efficiency in the guide is estimated to be >10% for approximately 1 mu J 20 ns pulsed excitation.<>