摘要:

In this letter, we report the observation of N-shaped negative-differential-resistance (NDR) characteristics in a SiC/Si heterostructure diode. The typical NDR in this device has a peak-to-valley current ratio (PVCR) of 44 and a high peak current of 4.8 mA at room temperature. A possible model based on the multi-tunneling process was proposed to explain the origin of the NRD in this device. The most attractive feature of this device is its high-temperature NDR characteristics. An obvious NDR with a PVCR of as high as 9 is obtained at 200 °C, indicating that this SiC/Si heterostructure NDR diode is promising for high-temperature electronic applications. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121526

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A comparative study ofn-n+andp-n+semiconductor heterojunctions has been done using the surface photovoltage spectroscopy (SPS) in the chopped light geometry. Heterojunctionsn-Al0.4Ga0.6As/n+GaAs andp-Al0.37Ga0.67As/n+GaAs and substraten+doped GaAs have been studied in the wavelength range 600–1000 nm. A sharp decrease in SPS at the band-gap energies of AlGaAs and GaAs with a broad peak in the subband-gap region of GaAs has been observed. The magnitude of surface photovoltage (SPV), for a constant photon flux forn-n+samples, is less by more than two orders of magnitude than that forp-n+samples in the wavelength range 645–870 nm. Changes in the dipole moments due to the redistribution of excess carriers in the space-charge regions are in opposite directions of then-n+heterojunctions giving less SPV, while forp-n+heterojunction, the changes in the dipole moments are in the same direction giving more SPV in comparison to then-n+samples. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121527

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We have verified that the condition of negative electron affinity (NEA) exists on hydrogen-terminated polycrystalline cubic boron nitride(c-BN)grown by the high-pressure high-temperature method using ultraviolet photoelectron spectroscopy. The NEA condition is thermally stable to 950 °C. At higher temperatures, the surface reverts to a positive electron affinity condition due to the desorption of surface bound hydrogen. Repeated annealing at high temperatures results in the degradation of the surface crystallinity, which manifests in the growth of a&pgr;→&pgr;*feature attributable tosp2-type bonds. Complete regeneration of initial valence band features and NEA conditions along with the suppression of the&pgr;→&pgr;*features can be achieved by subjecting the surface to atomic hydrogen etching. It is discovered that the He (II)-excited valence band spectra ofc-BNdisplay significant differences between the hydrogen-terminated and hydrogen-free surface. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121528

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Using deep-level transient spectroscopy (DLTS) and admittance spectroscopy we investigated nitrogen doped ZnSe and ZnSSe layers grown onp-type GaAs substrates by molecular beam epitaxy. Three major hole traps denotedT1,T2,andT3were observed with energy levels at 0.11, 0.46, and 0.56 eV from the valence band, respectively. Similar energy levels were observed in nitrogen doped ZnSSe except thatT1was at 0.12 eV from the valence band. A crude estimation of the 0.11 eV trap concentration obtained from DLTS data shows correlation with the free carrier concentration due to nitrogen. We attributeT1to a nitrogen acceptor which controls thep-type conduction in the materials. No other direct observations of this important acceptor level have been reported in the literature so far. The two remaining levels may originate from the nitrogen doping process. We also point out the effect of the series resistance observed in this kind of material. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121529

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Bridgman-grown, nominally undoped CdTe crystals were doped with Ag by implanting radioactive111Ag.Photoluminescence spectra of the crystals show a donor-acceptor pair (DAP) line at 1.491 eV. The decrease of the intensity of this line with a half life ofT1/2=(7.2±0.4)dis in good agreement with the half life of the&bgr;−decay of111Agto111Cdof 7.45d.This decrease is not caused by the aging behavior of Ag which was reported in the literature. The data show that the involved acceptor defect contains exactly one Ag atom and confirm the earlier assignment of the acceptor to theAgCddefect. Based on the DAP line at 1.491 eV, the spectra did not reveal a contamination of the CdTe crystals by stable Ag. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121530

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We present reflection THz-time domain spectroscopy measurements of the complex conductivity ofn-type, 0.038 &OHgr; cm GaAs andn-type, 0.22 &OHgr; cm Si wafers. These measurements clearly demonstrate the efficacy of the reflection technique on highly conductive, optically dense samples and approach the precision of THz–TDS transmission measurements. Because the THz-bandwidth, reflection measurements extend beyond the carrier collision frequency, we obtain direct measures of the mobility and the carrier number density. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121531

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

GaN nanocrystals with an average diameter of 4.5 nm±1.6 nm were synthesized by pulsed laser ablation of a gallium metal target in a nitrogen atmosphere. Transmission electron microscopy and selected area electron diffraction confirmed the hexagonal structure and size of the nanocrystals. Optical absorption and photoluminescence spectroscopy revealed quantum confined excited states in the nanocrystalline samples with features at 4.43 eV (280 nm) and 5.47 eV (227 nm). ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121532

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

It has been claimed that the variation of currentIwith voltageVin an organic light emitting diode (LED), based on either metal chelate complexes or conducting polymers, is explained by shallow traps that trap carriers propagating in the conduction or valence band. However, because these are disordered materials all states are localized. We show that it is possible to fit the dependence ofIonVand on film thickness without explicitly introducing traps, but taking their effect into account by including the mobility variation with the electric field that arises from the distribution in energy of the localized levels. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121533

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The annealing kinetics of stress-induced leakage current in ultrathinSiO2has been quantitatively investigated after high temperature bakes. We have found that the defects at the origin of the stress induced-leakage current can be fully annihilated and that it is possible to generate and anneal them several times without deterioration of the oxide quality. Moreover, the activation energy and diffusion coefficient deduced from the recovery time constant of the annealing kinetics are found nearly independent of the oxide thickness. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121534

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Preamorphous damage inp-type Si implanted with MeV Si ions and annealed at elevated temperature is characterized using deep level transient spectroscopy (DLTS) and transmission electron microscopy (TEM).P-type Si was implanted with 4 MeV Si at doses from1×1013to1×1014cm−2and annealed at 800 °C for 15 min. For doses below this critical dose, a sharp peak is observed in the DLTS spectrum, corresponding to the signature of point defects. Above the critical dose, a broad DLTS peak is obtained, indicating the presence of extended defects. This behavior is found to be consistent with TEM analyses where extended defects are only observed for doses above the critical dose. This suggests a critical dose at which point defects from implantation act as nucleating sites for extended defect formation. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121535

出版商:AIP    

年代:1998

数据来源: AIP