摘要:

Nucleation kinetics and spatial distribution of spherulitic clusters can be determined from growth rate and cluster size measures. This method presented here was applied to the nucleation of disk‐shaped PtSi clusters which grow in solid phase on nitridized Si substrates. It shows that the nucleation occurs in three modes corresponding to three kinetic regimes. A first nucleation phenomenon occurs at the beginning of the annealing on low‐density (∼102cm−2) preferred sites which are not randomly distributed in the plane and probably linked to defects. Then a steady state of nucleation on preferred sites, which are randomly distributed with a density of about 104cm−2, is observed. A third phenomenon of nucleation is distinguished by a nucleation rate which exponentially increases with time. This ‘‘avalanche state’’ is linked to the presence of microclusters, the density of which can reach 107cm−2. It depends on temperature and on the ratio of platinum layer thickness to silicon nitride thickness.

ISSN:0021-8979    

DOI:10.1063/1.337065

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A vertical cold‐wall low‐pressure metalorganic chemical vapor deposition system is used for the growth of Sn‐dopedn‐type GaAs epilayers. Smooth and specular Sn‐doped GaAs epilayers can be easily grown. Van der Pauw Hall measurement, andI‐VandC‐Vcharacteristics show that tetraethyltin is a suitable source for GaAsn‐type dopant. Sn surface accumulation has been observed from Auger electron specroscopy (AES) and secondary ion mass spectrometry (SIMS) measurements. From infrared spectroscopy (IR) examination of the deposit on the quartz reactor wall, the decomposition of TEG is incomplete. The results of selective epitaxial growth indicate that the GaAs growth from TEG is controlled by surface kinetics. Tetraethyltin can enhance the growth rate of GaAs and decrease the As/Ga ratio and also EL2 concentration. A EL2 model is proposed.

ISSN:0021-8979    

DOI:10.1063/1.337066

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

WSixfilms of three different compositions (X>2.0) were deposited by chemical vapor deposition onto polysilicon and Si3N4coated substrates and subsequently annealed in N2at 1000 °C. The redistribution of the excess Si was studied using Auger depth profiling and cross‐sectional scanning electron microscopy techniques. For polysilicon sublayers the excess Si segregates to the polysilicon interface with a resulting increase in polysilicon thickness and decrease in WSixthickness in proportion to the excess Si content. For Si3N4sublayers the excess Si precipitates within the WSixlayer, but preferentially toward the free surface. Changes in surface and interface topography resulting from the Si redistribution are presented. The kinetics of the Si redistribution observed in the depth profiles are correlated with resistivity measurements.

ISSN:0021-8979    

DOI:10.1063/1.337067

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Electron spectroscopic comparison of the C‐rich SiC(0001¯) and Si‐rich SiC(0001) surfaces after cleaning and disordering by Ar+ion sputtering and subsequent annealing is reported. The chemical behavior of the two disordered surfaces differs significantly. Three distinct temperature regions with different carbon surface segregation kinetics are discernible on SiC(0001¯). On SiC(0001) only one temperature region for C‐segregation is observed. Below 900 K, no spectroscopic differences between the two crystal surfaces are observed. Between 900 and 1300 K, both faces are terminated by a surface graphite layer and the C‐rich face shows an additional carbon surface segregation process. Above 1300 K, the C‐terminated surface graphitizes at a higher rate than the Si‐terminated surface. Massive graphitization on both surfaces above 1300 K is attributed to Si(g) sublimation from the SiC surfaces. The results demonstrate that extensive surface disordering of polar SiC faces does not destroy the memory for the polarity of the original crystal insofar as high‐temperature surface chemistry is concerned.

ISSN:0021-8979    

DOI:10.1063/1.337068

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The density of states of the valence and conduction bands ofn‐type GaAs has been calculated for a donor density of 1017cm−3at 300 and 20 K. Both the donor‐carrier and carrier‐carrier interactions have been included. Band tails appear on both bands and the energy gap is narrowed. Calculations were also performed for a donor density of 1015cm−3at 300 and 20 K. These results show the formation of an impurity band at 20 K, whereas a band tail exists at 300 K.

ISSN:0021-8979    

DOI:10.1063/1.337069

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A new technique for deriving the electron mobility as minority carriers in semiconductor materials is introduced. The technique is based on the modulation of the Hall voltage through the introduction of a low‐level optical injection. The photogenerated excess carriers produce a signal which is a function of the magnetic field, the carrier mobilities and concentrations, and the concentration of excess carriers and thus to their lifetime. The measurement is easy to implement and it can be performed along with the measurement of the Hall coefficient and the conductivity. The only modification needed in a conventional galvanomagnetic setup is the introduction of a chopped low‐intensity laser. Using these three simultaneous measurements, we determined the equilibrium carrier concentrations, the two mobilities, and the effective excess carrier lifetime ofp‐type HgCdTe narrow gap semiconductor. This novel technique allows us to present the mobility of electrons as minority‐carrier throughout the temperature range of 13.6–300.2 K in this material.

ISSN:0021-8979    

DOI:10.1063/1.337070

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The quality and reliability of predictions from numerical simulations of GaAs/AlGaAs devices, such as heterojunction bipolar transistors, depend on model parameters. These parameters include the variations with doping and carrier concentrations of the valence‐ and conduction‐band edges and of the effective intrinsic carrier concentrations for heavily dopedp‐ andn‐type gallium arsenide. The Klauder self‐energy method is used to calculate the effects of interactions among carriers and dopant ions in heavily doped GaAs at 300 K. The carrier‐carrier interactions of exchange and correlation are estimated by interpreting optical‐absorption measurements and by calculations based on degenerate theory. When densities exceed 1019cm−3inp‐type and 1017cm−3inn‐type gallium arsenide, carrier‐dopant ion interactions and carrier‐carrier interactions become of the same order of magnitude and should be included in calculations of band‐structure changes and of properties which depend on the density of states, such as carrier transport and effective intrinsic carrier concentrations.

ISSN:0021-8979    

DOI:10.1063/1.337071

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

We have studied hole transport in amorphous As2Te3(a‐As2Te3) films by time‐of‐flight (TOF) and transient field‐effect (TFE) measurements. Since the mobility gap of this material is small, the TOF experiments could be carried out only at temperatures below 200 K. Transport appears to be dispersive, due to multiple trapping in the valence‐band tail. In order to extend the observations to higher temperature and longer times, we have developed a new technique, the TFE. A careful analysis shows that TFE data can be dispersive even if transport is nondispersive, because a long thin‐film transistor is equivalent to a transmission line. Nevertheless, the resulting data can be used to characterize the density of states beyond the mobility edge. We find that multiple trapping indeed predominates, and the valence‐band tail is exponential with a characteristic temperature of about 290 K. This is somewhat lower than indicated by TOF data, probably because hopping transport predominates at low temperatures. The long‐time transients can be associated with either neutral defect interconversion and a continuous distribution of decay times or deep traps near the semiconductor‐oxide interface. However, the ultimate disappearance of the response reflects the effects of Fermi‐level pinning by valence alternation pairs with a negative effective correlation energy, as expected.

ISSN:0021-8979    

DOI:10.1063/1.337072

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

We present preliminary results of a study of defects in GaAs‐AlGaAs superlattices using deep‐level transient spectroscopy (DLTS). A dramatic difference is observed between the DLTS spectra of two superlattices when the superlattice period is doubled. This is explained by the presence of miniband conduction in the case of the smaller period and its absence in the case of the larger, and by the consequent difference in the distribution of electrons in the superlattice. Observed activation energies must be reinterpreted for comparisons to bulk material.

ISSN:0021-8979    

DOI:10.1063/1.337073

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The nature of ion bombardment damage on Si surface barriers has been studied with 20‐keV, variable‐dose Ar ion implantation and controlled removal of the damaged Si surface layers prior to Schottky metallization. The electrical properties of resultant Al/p‐Si Schottky diodes are found to be insensitive to the removal of the first few tens of nm of Si, and subsequent etching of over 100 nm is needed to restore the Schottky barrier height. Low‐temperatureI‐Vcharacteristics of these devices further reveal the presence of ion damage‐induced polycrystalline regions, confirming recent observations under high‐resolution electron microscopy.

ISSN:0021-8979    

DOI:10.1063/1.337074

出版商:AIP    

年代:1986

数据来源: AIP