摘要:

It is shown that a simple kinetic model can account for existing data both on the formation of the native defect EL2 in the temperature range 644–800 °C in GaAs samples from which EL2 was eliminated by a 1200 °C anneal/quench and on the disappearance of EL2 during anneals in the temperature range 1000–1200 °C. Our analysis suggests that EL2 consists ofVGabound to an unidentified ‘‘kernel’’ which, if not actually stable at temperatures up to 1200 °C, forms relatively rapidly at the lower temperatures and dictates the final concentration of EL2 in the sample. The change in enthalpy involved in the capture or release ofVGaby the kernel is estimated to be 5.6 eV.

ISSN:0021-8979    

DOI:10.1063/1.348404

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Deep‐level defects in as‐grown, ingot‐annealed, and wafer‐annealed samples of semi‐insulating gallium arsenide have been investigated by spatially resolved measurements of room‐temperature photoluminescence, infrared absorption, free‐carrier lifetime, and resistivity. High‐temperature ingot annealing mainly causes a homogenization of the EL2 distribution. Rapid cooling from a wafer annealing process atT>900 °C suppresses the formation of the previously lifetime‐limiting recombination center. After wafer annealing the EL2 defect may be the dominant recombination center, while in as‐grown and ingot‐annealed material lifetime is limited by a different trap. There is experimental evidence that this trap is related to the 0.8‐eV luminescence band and that its density is spatially anticorrelated to the EL2 distribution. Based on lifetime measurements and a correlation of EL2 and photoluminescence topographs, we developed a recombination model, which explains the relationship between defect densities, and photoluminescence. The effect of surface recombination is described by a numerical calculation.

ISSN:0021-8979    

DOI:10.1063/1.348405

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The aim of this research has been to investigate the role of the second law in thermoelectric phenomena. Considering the thermoelectric generator as a heat engine cycle process, the Kelvin relations for the thermoelectric circuit are derived from the energy balance and from the second law without using reversibility or equilibrium assumptions. A new formula has been derived for the thermal efficiency of the thermoelectric generator, also taking into account Thomson heat. An equation for maximum efficiency is derived and a representative numerical example of this equation is presented.

ISSN:0021-8979    

DOI:10.1063/1.348406

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The photovoltaic characteristics of optimized iodine‐doped thin‐film sandwich cells of the structure Al/Al2O3/magnesium tetraphenylporphyrin/Au, fabricated and tested under high vacuum, are reported. The action spectra of the short‐circuit photocurrent show that only light absorbed near the Al‐Al2O3electrode, to a depth of ∼70 nm in the porphyrin layer, is effective in producing charge carriers, consistent with the presence of a depletion region at this contact. Comparison of observed and modeled action spectra indicate an underlying enhancement of carrier generation which increases with increasing excitation energy above ∼2 eV. The photovoltaic efficiency increases with decreasing porphyrin thickness between 200 and 100 nm. Maximum values of &eegr;wh=1×10−3 %, &eegr;’&egr;=7×10−2 % and &fgr;&egr;=4.3 % are obtained for a 100‐nm thick film. For the thinner cells, the photocurrent varies linearly with light intensity up to 106 mW/cm2, indicating that little recombination of charge carriers occurs during transport to the electrodes. The porphyrin films degrade rapidly in the presence of oxygen/water vapor; however, the stability of the films and devices is good under vacuum. Possible mechanisms of charge‐carrier generation are discussed.  

ISSN:0021-8979    

DOI:10.1063/1.348407

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The thermoelectric properties of 28 sintered Si0.8Ge0.2alloys, heavily doped with either boron or phosphorus and prepared from powders with median particle sizes ranging from about 1 &mgr;m to over 100 &mgr;m, have been determined from 300 to 1300 K. The thermal conductivity decreases with decreasing particle size, however, the figure of merit is not significantly increased due to a compensating reduction in the electrical conductivity. The thermoelectric figure of merit is in good agreement with results of Dismukesetal. [J. Appl. Phys.10, 2899 (1964)] on similarly doped alloys prepared by zone‐leveling techniques. The electrical and thermal conductivity are found to be sensitive to preparation procedure while the Seebeck coefficient and figure of merit are much less sensitive. The high‐temperature electrical properties are consistent with charge carrier scattering by acoustic or optical phonons.

ISSN:0021-8979    

DOI:10.1063/1.348408

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The effect of heat treatments on the structure and composition of a system consisting of a conductive outer layer made of Al(0.8% Si) thin film, TiW(30:70 at. %) thin film as a diffusion barrier, and a polycrystalline Si substrate was studied. It was established that heat treatments at temperatures ranging between 400 and 500 °C led to the diffusion of Si and Al through the TiW layer, following which Al diffused into the polycrystalline Si, while Si diffused into the Al film. The silicides of TiSi, TiSi2, and intermetallic compounds of Al3Ti and WAl12were formed at the Al/TiW interface as a result of the 30‐min heat treatment at temperatures ranging between 450 and 500 °C.

ISSN:0021-8979    

DOI:10.1063/1.348409

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Lateral degrees of freedom in resonant tunneling heterostructure devices are investigated in a model which omits the usual assumption that the electric field and current density are laterally uniform. Relaxation of spatially nonuniform configurations of field and current into the usual uniform configurations is examined. For certain device parameters and operating conditions, stable nonuniform configurations are found in addition to the conventional uniform configurations. An eigenvalue criterion for stability is established. The possibility of nonuniform configurations with spatially localized oscillation is also discussed.

ISSN:0021-8979    

DOI:10.1063/1.348379

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The chemistry of the (NH4)2Sx‐treatedn‐GaAs (100) surfaces has been studied using synchrotron radiation photoemission spectroscopy. Ga 3d, As 3d, and S 2pphotoemission spectra are measured before and after annealing in vacuum with a photon energy of about 210 eV, where S 2pcore level spectra can be sensitively detected. It is found that Ga‐S, As‐S, and S‐S bonds are formed on the as‐treated GaAs surfaces, and that stable Ga‐S bonds become dominant after annealing at 360 °C for 10 min in vacuum. The thickness of the surface sulfide layer is reduced from about 0.5 to 0.3 nm by annealing. The surface Fermi‐ level position of the as‐treated surfaces is determined to be about 0.8 eV below the conduction band minimum, which is about 0.1 eV closer to the valence band maximum than that of the untreated surfaces. A Fermi‐level shift of 0.3 eV toward a flat band condition is also observed after annealing. It is found that the Ga‐S bonding plays an important role in passivating GaAs surfaces.

ISSN:0021-8979    

DOI:10.1063/1.348380

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

This work investigates the characteristics of PtSi‐silicidedp+nshallow junctions fabricated by implanting BF+2ions into either the Pt/Si (ITM scheme) or the PtSi/Si (ITS scheme) structure followed by annealing in N2furnace at temperatures from 650 to 800 °C. For a structure with Pt film of 30 nm thickness or PtSi film of 60 nm thickness, the implantation energy ranges from 40 to 80 keV with a dose ranging from 1×1015to 1×1016cm−2. For the ITS samples with BF+2implantation at 40 keV, all ions are confined in the PtSi layer; therefore, only a modified Schottky junction is formed by the diffusion of boron atoms from the PtSi film during the annealing. The junction depth may be as shallow as 30 nm from the PtSi/Si interface. A completep+njunction is formed for the ITM samples with implantation at 40 keV as well as all the samples implanted at 80 keV. The junction thus obtained has a forward ideality factor lower than 1.02 and a reverse current density less than 0.2 nA/cm2at −5 V. Activation energy measurement indicates that most of the implantation damages have been recovered after annealing at a temperature as low as 700 °C. The reverse area and peripheral leakage current density are separated by measuring diodes of different perimeter/area ratio. For good samples, the reverse peripheral current comes from the surface generation current within the depletion region underneath the field oxide. All of the experimental results reveal that either Pt or PtSi film can be employed as an efficient barrier film in the ITM/ITS technique to form excellent and ultrashallow junctions with a low thermal budget.

ISSN:0021-8979    

DOI:10.1063/1.348359

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The Pd‐In‐Ge nonspiking Ohmic contact ton‐GaAs has been investigated using the transmission line, the Kelvin, and the Cox and Strack structures. It has been found that a layered structure of Pd/In/Pd/n‐GaAs with 10–20 A˚ of Ge imbedded in the Pd layer adjacent to the GaAs can lead to a hybrid contact. When the Ohmic formation temperature is above 550 °C, a layer of InxGa1−xAs doped with Ge is formed between the GaAs structure and the metallization. When the Ohmic formation temperature is below 550 °C, a regrown layer of GaAs also doped with Ge is formed at the metallization/GaAs interface. The contact resistivity of 2–3×10−7&OHgr; cm2for this contact structure is nearly independent of the contact area from 900 to 0.2 &mgr;m2. Low‐temperature Ohmic characteristics and thermal stability are also examined.

ISSN:0021-8979    

DOI:10.1063/1.348360

出版商:AIP    

年代:1991

数据来源: AIP