摘要:

Temperature dependence of sharp photoluminescence and absorption peaks, which originate from then=1 free heavy‐hole exciton, in a ZnSe–ZnS strained‐layer superlattice (Lb=50 Å andLw=25 Å) with a multiple quantum‐well structure has been investigated. A dominant mechanism responsible for broadening in the excitonic linewidth below 85 K is an ionized donor impurity scattering of free excitons that occurs in addition to the acoustic phonon scattering. On the other hand, it is suggested that the linewidth of the excitonic absorption peaks at high temperature is attributed to the scattering of free excitons withLOphonons. Stark shifts and a concomitant quenching in intensity of the exciton line were observed under electric fields.

ISSN:0734-211X    

DOI:10.1116/1.584601

出版商:American Vacuum Society    

年代:1989

数据来源: AIP

摘要:

The electrical properties of pseudomorphic epilayer–epilayer ZnSe/GaAs heterointerfaces, grown by molecular‐beam epitaxy, have been investigated by capacitance versus voltage (C–V) and current versus voltage measurements. Undoped stoichiometric ZnSe (<1000 Å), exhibiting high resistivity, performs the function of the insulator in these metal–insulator–semiconductor capacitors. TheC–Vcharacteristics of the annealed Au/ZnSe/p‐GaAs capacitors are nearly ideal, exhibiting an interface state density (2.5×1011cm−2) which compares favorably with the densities reported at typical (Al,Ga)As interfaces. The occurrence of both hole accumulation (forp‐type GaAs) and inversion (forn‐type GaAs) at the ZnSe/GaAs heterointerface indicates the presence of a substantial valence‐band offset. The lack of accumulation or inversion layers for electrons suggests a relatively small conduction‐band discontinuity.

ISSN:0734-211X    

DOI:10.1116/1.584602

出版商:American Vacuum Society    

年代:1989

数据来源: AIP

摘要:

We demonstrate that quasi direct band gap Si1−xGex/Si superlattices can be obtained by suitable choices of layer thicknesses. We calculate strain dependent conduction‐band offsets as functions of the substrate alloy concentration, and of the epilayer alloy concentration. Optical matrix elements are computed for Si0.5Ge0.5/Si superlattices grown on Si0.75Ge0.25buffer layers with superlattice layer thicknesses of 4 to 24 monolayers. We find that optical absorption and emission strengths can vary by three to four orders of magnitude for layer thickness variations as small as 1–2 monolayers, suggesting that layer thicknesses must be controlled to within one monolayer to obtain enhanced optical properties. Typical optical matrix elements calculated for these Si1−xGex/Si superlattices are three to four orders of magnitude larger than for bulk Si or Ge, but, are still three orders of magnitude smaller than for direct band gap materials such as GaAs.

ISSN:0734-211X    

DOI:10.1116/1.584603

出版商:American Vacuum Society    

年代:1989

数据来源: AIP

摘要:

We have studied the photoreflectance (PR) spectra from a molecular‐beam epitaxially (MBE) grown heterostructure consisting of 200 nm of Ga0.83Al0.17As , a 800‐nm GaAs buffer layer on a semi‐insulating (SI) 〈100〉 (LEC) GaAs substrate. By varying both the pump beam wavelength and modulation frequency we are able to identify the component layers, their quality, and the quality of the various interfaces. In this study we find evidence for a low density of interface states between the GaAs buffer layer and the GaAlAs layer, and a relatively large density of interface states, between the substrate and buffer layers. These states, previously observed by deep‐level transient spectroscopy (DLTS) of doped structures, are presumably associated with the interface produced by MBE growth on etched and air exposed substrates. However, in our experiment since the substrate is semi‐insulating and the buffer layer is undoped, it is difficult to resolve these states spatially byC–Vtechniques. Our results show that the PR technique can be used to characterize low conductivity or semi‐insulating structures such as enhancement mode metal–semiconductor field effect transistor (MESFET) and high electron mobility transistor (HEMT) type devices and it may be useful for theinsitucharacterization of epigrown surfaces and interfaces.

ISSN:0734-211X    

DOI:10.1116/1.584604

出版商:American Vacuum Society    

年代:1989

数据来源: AIP

摘要:

The CdS/InP(110) heterojunction, which is one example of a lattice matched combination among the junctions between II–VI and III–V compound semiconductors, was studied on molecular‐beam epitaxy grown samples on cleaved as well as ion bombarded and annealed InP(110) surfaces. The junctions were characterized by core and valence photoemission using synchrotron radiation, Auger electron spectroscopy (AES), and low‐energy electron diffraction (LEED). Deposition of CdS on cleaved InP(110) surfaces led to layers which exhibited good laminar growth, and gave sharp LEED patterns with fairly low background, with a periodicity of the InP(110) substrate lattice, demonstrating that CdS was grown in the metastable zinc‐blende conformation. On InP surfaces cleaned by ion bombardment and annealing, however, growth of crystalline CdS could not be achieved. From the evaluation of band bending upon CdS growth on the basis of core level, line‐shape deconvolution, and the changes in the valence‐band emission, we have derived a valence‐band offset in this system of −0.77±0.1 eV; this means that this heterojunction is of the straddling type, in disagreement with previous data fromC–Vmeasurements which indicated a staggered lineup. We compare our result for the band lineup with current theoretical models.

ISSN:0734-211X    

DOI:10.1116/1.584605

出版商:American Vacuum Society    

年代:1989

数据来源: AIP

摘要:

X‐ray photoemission spectroscopy (XPS) has been used to measure the unstrained valence‐band offset ΔEvfor thex=0 andx=1 end points of the InxGa1−xAs/InP (100) heterojunction system. Although the GaAs/InP (100) and InAs/InP (100) pseudomorphic interfaces investigated are strained because of lattice mismatch, the ΔEvvalues obtained by the XPS measurement analysis used are interpreted as characteristic of an unstrained interface. Strain‐free values of ΔEv(GaAs/InP)=0.19 eV and ΔEv(InAs/InP)=0.31 eV are reported. A linear interpolation of thesex=0 andx=1 unstrained values gives ΔEv(In0.53Ga0.47As/InP)=0.25 eV (ΔEc/ΔEv=58/42) for the lattice‐matched interface.

ISSN:0734-211X    

DOI:10.1116/1.584606

出版商:American Vacuum Society    

年代:1989

数据来源: AIP

摘要:

Predictions of band offsets assign a type‐II offset for the GaAs–InP interface without inclusion of strain effects, with the conduction‐ and valence‐band‐edge offsets approximately given by 0.4 and 0.3 eV, respectively. It has been demonstrated recently that pseudomorphic GaAs grown on [100]‐oriented InP also has a type‐II interface, but with the conduction‐band offset reduced by the hydrostatic deformation potential of GaAs. Poisson’s ratio in GaAs for [111]‐directed uniaxial stress is smaller by 40% than the value for [100]‐directed stress. The lattice constant perpendicular to the growth interface is therefore not reduced as much for [111]growth compared with the [100]‐growth case, leading to a consequently larger shift of the conduction‐band‐edge energy. Based on the recently measured value of −9 eV for the conduction‐band‐edge hydrostatic deformation potential in GaAs, the band offset for pseudomorphic GaAs grown on (111) InP has been calculated to be type I. This material system should therefore show type II to type I conversion dependent on the growth direction of the pseudomorphic layer. The issues involved in the growth and measurement of GaAs grown on (111) InP are discussed briefly.

ISSN:0734-211X    

DOI:10.1116/1.584607

出版商:American Vacuum Society    

年代:1989

数据来源: AIP

摘要:

Photoluminescence and thermally modulated photoluminescence have been employed in thin single quantum wells in the InP/Ga1−xInxAs/InP system (0≤x≤1). The potential use of these methods to estimate conduction and valence‐band offsets in strained‐layer heterostructures is discussed.

ISSN:0734-211X    

DOI:10.1116/1.584608

出版商:American Vacuum Society    

年代:1989

数据来源: AIP

摘要:

We have now demonstrated that the ratio of the activation enthalpies for nearest neighbor hopping of the two types of vacancy in InP are in the 4 to 1 ratio of the masses of the atoms that hop and are in good agreement with the values predicted by the ballistic model (BM), which identifies the activation enthalpy as a kinetic energy. A consequence is that relatively light atoms should hop to second neighbor vacancy sites as easily as heavy atoms hop to nearest neighbor vacancies, and do so without the complication of forming or annihilating antisites. For example, in GaAs B, C, N, Al, Si, and P are predicted to hop to second neighbor sites as easily as As hops to a first neighbor site. Of course, they hop to nearest neighbor sites even more readily. The import of this on the array of point defects predicted to occur as a heterojunction anneals is rather complex. Experiment supports our contention of complexity. For example, in As rich,n‐type AlGaAs Meietal. reportD(Al)∝n1 exp(−2.9 eV/kT) if the doping is with Te butD(Al) ∝n3 exp(−4 eV/kT) if the doping is with Si, wherenis the free electron density. We have studied the Al diffusion in AlGaAs with the aid of a microcomputer simulation that works out the complex consequences of one’s assumptions re thermochemical parameters at the atomic level. Our previously published BM assumptions lead to the conclusion that Si promotes the conversion of Ga vacancies to trivacancies while Te does not; they also identify 2.9 eV as the sum of the Ga second‐neighbor hopping enthalpy and the enthalpy of formation of single negative Ga vacancy inn‐type GaAs and identify 4 eV as the sum of the enthalpy of formation of the trivacancy plus its nearest neighbor hopping energy in GaAs. The simulation also finds that Al by itself converts As vacancies to trivacancies plus metal antisite. It shows the trivacancies to diffuse very rapidly and to entrain Al.We propose that the cation sublattice dominance of Si induced host interdiffusion follows from this entrainment. We also suggest these complexes are related to DX and account for the anomalous variation of the parameters of that defect with Al concentration. Except for the assumption that the hopping kinetic energy be proportional to the mass of the hopping atom, the conclusions stated above are insensitive to the precise values of atomic level parameters assumed. Quantities such as activation energies for macroscopic diffusion are sensitive to the precise values and some of these are either poorly determined or controversial. More simulation than we have accomplished to date is required to establish the relation between precise atomic level values and observable macroscopic quantities.

ISSN:0734-211X    

DOI:10.1116/1.584609

出版商:American Vacuum Society    

年代:1989

数据来源: AIP

摘要:

We report photoemission studies of GaAs(100) surfaces treated with H2S. Our high‐resolution core level photoemission data show that these surfaces are completely terminated by a GaSxspecies and the treated surface is stable in air or water. Thus a H2S treatment might result in better device quality surfaces and interfaces than the surfaces prepared by recently proposed chemical treatments involving Na2S or (NH4)2S.

ISSN:0734-211X    

DOI:10.1116/1.584610

出版商:American Vacuum Society    

年代:1989

数据来源: AIP