摘要:

Spatially resolved carrier lifetimes have been measured at the same grain boundary using a series of adjacent samples doped to different levels by neutron transmutation. The samples had dopant concentration levels between 1013and 1017atoms/cm3. The carrier lifetime was measured using a contactless microwave absorption technique to monitor the decay of photoconductivity which allowed us to perform either isothermal or isochronal annealing to remove the damage caused by irradiation. An optimum anneal of 30 min at 700 °C resulted in almost full recovery to the lifetime before irradiation. A short laser pulse of wavelength 900 nm was focused to a 0.3‐mm‐diam spot on the samples. Lifetimes of two different sets of carriers were measured, the bulk carrier lifetime at the center of a grain and the carrier lifetime at a grain boundary. This latter carrier lifetime involves both fast and slow recombination mechanisms. The slow decay mechanism is due to interface states at the grain boundary. The fast recombination lifetime was found to be of the same order as the bulk recombination lifetime (of the order of 1 &mgr;s) and the slow one was of the order of 1 ms. Doping levels up to 1016atoms/cm3show no significant effect on the measured bulk carrier lifetime.

ISSN:0021-8979    

DOI:10.1063/1.337258

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A pair of coupled, nonlinear integro‐differential equations, which exactly describe the transient current produced by the drift and collection of a swarm of space charge in a medium between two electrodes, has been derived for a single charge carrier species using a field‐independent mobility model. The equations represent the solution of the mathematical problem involving arbitrary space‐charge sizes and distributions coupled with the effects of the inherent time constants of the physical system. Computer‐generated numerical solutions, for the special case of the initial charge distributions which correspond to steady‐state currents, are reported. The equations under these conditions can be decoupled to form a stiff third‐order differential equation. The numerical results indicate a possible scheme for correcting transient current waveforms, which are distorted by space‐charge fields, in order to obtain the proper, ideal times of flight needed for true mobility measurements.

ISSN:0021-8979    

DOI:10.1063/1.337259

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Electronic transport properties of heavily doped arsenic implanted silicon are reported. Hall mobility and sheet resistance as functions of temperature and frequency have been carried out both on annealed and as‐implanted silicon films. The small values of the observed Hall mobility and strong frequency dependence of the transport coefficients emphasize the drastic alteration of nonannealed material. A semiquantitative analysis of the results is conducted using both short‐range and long‐range disorder considerations (hopping and percolation).

ISSN:0021-8979    

DOI:10.1063/1.337260

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Thermoluminescence, phosphorescence, and ac conductivity measurements have been performed at room temperature on as‐grown or Li‐, Na‐, and Cu‐ electrodiffused synthetic quartz, beta or x ray irradiated, to confirm the ionic nature of the charge carriers in the radiation‐induced conductivity (RIC). Comparison between RIC and phosphorescence time dependence has allowed us to propose a mechanism for the annealing process of the RIC.

ISSN:0021-8979    

DOI:10.1063/1.337261

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The conduction‐band discontinuity (&Dgr;Ec) between In0.53Ga0.47As and In0.52Al0.48As is determined by current‐voltage measurements onn+‐InGaAs/InAlAs/n−‐InGaAs capacitors. Current is found to be dominated by thermionic emission conduction down to 180 K. Barrier heights are determined from the slope of ln(J/T2) vs 1/Twhere good straight‐line fits are obtained in the thermionic emission range. After correcting for the Fermi level a conduction‐band discontinuity of 0.51±0.04 eV is obtained representing 70% of the total band‐gap discontinuity. Furthermore, capacitance‐voltage measurements are fit to classical capacitance‐voltage theory and show that no charge is present in the InAlAs insulating layer.

ISSN:0021-8979    

DOI:10.1063/1.337262

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

We measure picosecond photoinduced absorption in a low‐defect sample of intrinsic hydrogenated amorphous silicon. Our results indicate that both the imaginary and real parts of the complex index of refraction contribute to the observed decay of the induced transmittance. We present methods for obtaining the undistorted decay of the induced absorption. We show that the decay of the induced absorption depends strongly on the peak carrier density and the repetition rate of the excitation source. The photoinduced absorption decays are consistent with the model for dispersive transport in amorphous materials.

ISSN:0021-8979    

DOI:10.1063/1.337263

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Novel metal‐oxide‐semiconductor structures with very large areas have been used together with the vacuum emission and carrier separation techniques to study electron heating down to low fields (≊1 MV/cm) and out to large oxide thicknesses (5200 A˚). At electric field magnitudes between 1.5 and 2.0 MV/cm, the threshold field for the onset of electron heating in silicon dioxide is observed. This onset is independent of oxide thickness and composition. Its value is consistent with all of the current theoretical calculations. At fields near threshold, a minimum average electronic energy of ≊1.0 eV is shown to be necessary to observe emission of the electrons into vacuum. Although the general trends in most of the data are approximately independent of oxide thickness out to 5200 A˚, certain thick oxide samples with higher water content and lower physical density do show deviations from stabilization at higher fields, particularly in the vacuum emission experiments. Also, the data tend to appear ‘‘noiser’’ as the oxides become thicker. These apparently hotter electronic distributions are discussed in relationship to the proposed formation of microscopic channels in the oxide bulk.

ISSN:0021-8979    

DOI:10.1063/1.337264

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The vacuum emission technique has been used to study electron transport and heating in silicon nitride and silicon oxynitride. The experimental results are compared to data for silicon dioxide in which all the conduction‐band electrons can gain several eV of energy at electric fields greater than 2 MV/cm. Although average electron energy as a function of electric field curves are very similar to silicon dioxide, the total number of electrons which can be heated to energies greater than 2 eV is greatly reduced because of the increased trapping in these films. Reduction in hot electrons due to increased trapping is correlated to increasing nitrogen content through the oxynitride phases to silicon nitride. Trapping/detrapping on energetically shallow sites in the forbidden gap controls the bulk limited conduction in these films, and very few electrons are allowed to move freely in the conduction band.

ISSN:0021-8979    

DOI:10.1063/1.337265

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The modifications of the electronic properties of cleaved GaAs (110) surfaces induced by the oxygen adsorption have been studied by contact potential difference measurement. The oxygen exposure induces acceptor and donor surface states which pin the surface Fermi level at approximately 0.45 and 0.7 eV above the valence band forn‐ andp‐doped samples, respectively. Noticeable modifications &Dgr;&khgr; of the electronic affinity are also produced. The features of the states and the possible origins of &Dgr;&khgr; are discussed.

ISSN:0021-8979    

DOI:10.1063/1.337266

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

In spreading resistance analysis, which is a method usually employed in doping profiling, carrier spilling effects become evident in doping structures in the 0.1‐&mgr;m range. Profiles from spreading resistance analysis with such thin layers are to be interpreted rather in terms of ‘‘on bevel’’ carrier distribution than as actual doping profiles. Due to specific boundary conditions introduced by beveling, carrier spilling decisively depends on whether high‐low or low‐high transitions are considered. Using sample mounting both in standard and in upside down configuration high resolution of high‐low as well as low‐high transition is achieved.

ISSN:0021-8979    

DOI:10.1063/1.337267

出版商:AIP    

年代:1986

数据来源: AIP