摘要:

GaAs epilayers which are grown by molecular‐beam epitaxy under ‘‘normal’’ group III–V fluxes but at very low substrate temperatures contain as much as 1% excess arsenic. Upon annealing these epilayers at a temperature of 600 °C, the excess arsenic forms precipitates. We have undertaken a systematic study of the substrate growth temperature dependence of this incorporation of excess arsenic in both GaAs and Al0.3Ga0.7As epilayers. The substrate growth temperature was varied in increments of 25 °C from 225 to 375 °C after every 0.25 μm of film growth for a GaAs and an Al0.3Ga0.7As epilayer. Both epilayers were grown using a dimer arsenic source and a group V to total group III beam equivalent pressure ∼20. After growth the films were annealed for 1 h in the As2flux at a temperature of 600 °C. Cross‐sectional samples were than prepared by the ion thinning technique and examined by transmission electron microscopy (TEM). Both epilayers contained arsenic precipitates; this is the first observation of arsenic precipitates in an Al0.3Ga0.7As epilayer. The density of the arsenic precipitates in the two epilayers had a strong dependence on substrate growth temperature. Details of the film growth and of the TEM observations are reported.

ISSN:1071-1023    

DOI:10.1116/1.585742

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Exposure of GaAs crystals to solutions of organic thiols resulted in substantial reductions in nonradiative GaAs surface recombination rates. This process yielded improvements in steady state photoluminescence signals that were comparable to those obtained after a Na2S⋅9H2O (aqueous) treatment. Use of a series of thiols indicated that the chemically important surface electrical trap levels behaved as a polarizable, electron deficient center. X‐ray photoelectron spectroscopy indicated that the thiols did not remove excess As0nor form detectable levels of As2S3‐like phases, implying that neither of these factors is required for effective surface passivation chemistry.

ISSN:1071-1023    

DOI:10.1116/1.585743

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

This paper presents experimental results on sulfur bonding to etched GaAs surfaces which have an As/Ga ratio ranging from 0.6 to 6.0. The source of the sulfur was either a liquid solution of Na2S or (NH4)2S, or gaseous H2S applied in a N2purged glove box. Angle resolved x‐ray photoelectron spectroscopy (XPS) spectra was obtained from ∼40 different samples in order to determine the concentration of the various surface chemical species and their bonding state. Most of the experiments were conducted with H2S exposed samples at substrate temperatures from 30 to 350 °C. Sulfur is shown to bond to both Ga and As. The amount of bonding to each depends on the As/Ga ratio. This is true for both H2S and the liquid S solutions. Only one S–As bonding state was observed, independent of the S treatment process. S was observed to bond to elemental As and substrate As with the same binding energy and concentration. H2S exposed surfaces had a higher concentration of S than did those that were treated with Na2S or the (NH4)2S.

ISSN:1071-1023    

DOI:10.1116/1.585744

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Ballistic electron emission spectroscopy (BEES), a technique based on the scanning tunneling microscope (STM), was used to measure Schottky barrier heights of metals on cleavedn‐type GaP(110). The threshold voltagesV0for current detection in the semiconductor were found to be uniform to within ±0.02 V over the sample surface for any given metal on GaP. A transport model for the currentIccrossing the barrier, that includes both nonclassical transmission across the metal–semiconductor interface and electron scattering in the metal, yieldsIc∝(V−V0)5/2near threshold. The value ofV0extracted from the data, which represents the Schottky barrier height, depends somewhat on the details of the transport model. Our best estimates of the Schottky barrier heights, within ±0.03 eV, are 1.07 (Mg), 1.11 (Ni), 1.14 (Bi), 1.25 (Cu), 1.31 (Ag), and 1.46 eV (Au).

ISSN:1071-1023    

DOI:10.1116/1.585745

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

In order to extend the comparison of the initial stages of Schottky barrier formation to different surfaces of III–V semiconductors, we present here an investigation with low‐energy electron diffraction, Auger electron spectroscopy, and ultraviolet photoemission spectroscopy of In– and Ag–GaSb(100) interfaces at room temperature and after annealing. The initial GaSb surfaces exhibit a (3×2) structure. The low‐coverage growth of In and Ag is essentially two dimensional. It is followed by substantial islanding (In) especially after annealing. Band bending measurements show no significant movement of the Fermi level from its initial position near the valence band maximum.

ISSN:1071-1023    

DOI:10.1116/1.585746

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Surface scientists argue about the fundamental nature of Schottky barriers, or more precisely what determines the location of the Fermi level at semiconductor surfaces and interfaces. Electrical and materials engineers worry about how to make Schottky barrier diodes and gates to field effect transistors and the control of barrier heights. There is some interesting middle ground in which the location of the surface and interface Fermi level can, for example, determine semiconductor doping characteristics during crystal growth. In keeping with the trendy fashion of the 80’s to invent ‘‘catchy phrases’’ to describe marginally important new fields, we dub this middle ground as ‘‘surface Fermi level engineering.’’ Within the framework of this concept, we will discuss several interesting and well known examples of doping characteristics which are still somewhat mysterious. Specifically, we will address the following questions: (1) why is Ge doped GaAsptype when grown from Ga melts butntype when grown from Au melts? (2) why is low resistivityptype ZnSe, AlAs, and AlGaInP hard to make, and more importantly, how can we fix this problem? In addition we will describe how this concept relates to the electronic properties of a new type of GaAs, GaAs:As, which contains a high density of As precipitates.

ISSN:1071-1023    

DOI:10.1116/1.585703

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Luminescence experiments provide a powerful and nondestructive approach to theexsituinvestigation of semiconductor heterointerfaces which might be buried up to several μm below the surface in a given complex sample structure. Combined with the ability of taking images simply by scanning the exciting focused electron beam across the area under investigation, lateral fluctuations of electronic properties like the variation of the fundamental band gapEg(x,y) can be directly visualized by scanning cathodoluminescence (CL). The novel experimental approach, cathodoluminescence wavelength imaging (CLWI), which involves recording of a complete CL spectrum at every scanning position (x,y), yields direct 3D images of the atomic‐scale morphology of quantum wells (QWs) as sensed by the QW exciton: similar to the tip of a scanning tunneling microscope, the exciton samples the local fluctuations of QW thicknessLzand transforms this structural informationLz(x,y) into a spectral one, the lateral variation of band gapEg(x,y) and thus the CL emission wavelength λ(x,y). Topological maps of QW interfaces can thus be recorded at various positions and at various magnifications. The interface roughness can be investigated statistically at lateral resolution starting with the diameter of the QW exciton up to the mm regime. The same experimental principle for recording λ(x,y) andEg(x,y) maps is successfully applied for the analysis of patterned structures. In the nonlattice‐matched system GaAs on Si, the lateral strain variation causesEg(x,y) fluctuations and can thus be directly imaged by CLWI. Metalorganic chemical vapor deposition grown GaAs layers on micropatterned Si(001) substrates show strongly inhomogeneous doping with Si impurities. By means of CLWI the strong increase of this Si incorporation in the vicinity of free {111} surfaces is measured and Si concentration maps are recorded across the complete sample pattern.

ISSN:1071-1023    

DOI:10.1116/1.585704

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

We have conducted a thorough photoluminescence (PL) and PL time‐decay study of the interfacial passivating effects of metalorganic chemical vapor deposition prepared Al0.3Ga0.7As,n+‐doped GaAs, and Na2S surface barriers on epitaxial, high‐purity (n−) GaAs structures. We observe 300‐K radiative lifetimes, in such 10‐μm structures, of 2.5 μs, 800 ns, and 150 ns, respectively. These are to be compared with lifetimes of ∼2 ns for a single, ‘‘bare’’ GaAs surface with an Al0.3Ga0.7As rear surface barrier, and ∼0.5 ns for unpassivated epitaxial GaAs. Accompanying radiative efficiencies are 103–104higher in all of these epibased structures, and 102higher for Na2S, than for corresponding bare GaAs surfaces. Further, from detailed PL lifetime studies versus GaAs thickness, we find the lowest interfacial recombination velocities reported for any GaAs/AlxGa1−xAs structure, to date, of ≲40 cm/s, and, correspondingly, 0–1800 cm/s forn+/n−/n+all‐GaAs homostructures. Thus, virtually ‘‘surface‐free’’ structures are now achievable. In comparison, we find, at best, ∼5500 cm/s for Na2S, and typically 34 000 cm/s for bare GaAs surfaces. We conclude, on the basis of our detailed experimental study of a wide variety of samples, that these values provide truly reliable measures of surface recombination velocities for both surface types. We find an unambiguous determination of surface recombination velocities requires detailed examination of the minority‐carrier recombination kinetics versus temperature, together with minority‐carrier spatial transport properties. After demonstrating that minority‐carrier recombination kinetics in our ideal structures are truly ‘‘intrinsic,’’ and thus wholly unaffected by extrinsic processes, we examine the temperature dependence of band‐to‐band and free‐exciton recombination. We fully explain all intrinsic, free‐carrier recombination found in each structure, for temperatures of 40–300 K through rate equations appropriate to each structure. Similar low‐temperature (1.8–40 K) studies confirm dominant decay proceeds, here, by intrinsic free excitons.

ISSN:1071-1023    

DOI:10.1116/1.585705

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

We have used extensive photoluminescence (PL), PL time‐decay measurements, and detailed quantum mechanical modeling to both interpret and quantify the electronic and optical properties of free excitons localized near heterointerfaces. Through detailed spectroscopic measure of the recombination kinetics of the recently observed H‐band emission, we find this emission arises from the radiative decay of such weakly bound (≂0.5 meV) excitonic species confined to the hole‐attractive quantum potentials formed at thep–nheterointerfaces. Detailed measurements in virtually ‘‘interface‐free’’ double GaAs(n)/Al0.3Ga0.7As( p) heterostructures shows the effects of GaAs layer thickness upon the H‐band kinetics—thus confirming quasi‐2D excitons become effectively ‘‘shared’’ bybothheterointerfaces for sufficiently thin GaAs layers (400 μm) low temperature diffusion.

ISSN:1071-1023    

DOI:10.1116/1.585706

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

The Si(111)√3×√3:Al reconstruction has been studied by surface sensitive high resolution core level spectroscopy. It is shown that three components are needed to fit the Si 2pspectra. The Al 2pemission is found to consist of more than one component and it is argued that this is related to defects in the overlayer.

ISSN:1071-1023    

DOI:10.1116/1.585707

出版商:American Vacuum Society    

年代:1991

数据来源: AIP