摘要:

We have investigated molecular‐beam epitaxy (MBE) grown Si/SiGe hole resonant tunneling devices (RTDs) consisting of an unstrained Si0.5Ge0.5quantum well between two strained Si barriers. A peak current density of 104A/cm2and a peak‐to‐valley current ratio of 1.5:1 at 77 K and 2:1 at 4 K has been obtained. Using magnetotunneling measurements at 4 K, two resonances, corresponding to tunneling through the heavy hole and light hole states, have been identified with a light hole‐to‐heavy hole effective mass ratio of 3.2, suggesting that the hole band structure in the Si/Si0.5Ge0.5double barrier system is silicon‐like. We have examined devices with the same quantum well structure, but with different spacer thicknesses (90–360 Å) to study the influence of doping profile on the peak‐to‐valley current ratio and peak voltage position. Using these measurements, we have extracted the electric field across the quantum well for the different devices. These electric field values suggest that holes are exiting the quantum well at their saturation velocity of ∼107cm/s.

ISSN:1071-1023    

DOI:10.1116/1.584811

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

SimGenstrained monolayer superlattices (SMS) have been fabricated by molecular beam epitaxy (MBE) and characterized using photoluminescence. Symmetrically strained structures with different periodicities have been grown on top of Si1−xGexalloy buffer layers. Luminescence peaks below the Si energy bandgap have been observed. Superlattices on top of Si buffers with different substrate orientations have been prepared with thicknesses below the critical values in order to avoid generation of misfit dilocations. Energy band diagrams constructed based on the deformation potential and the envelope function approximation are used to explain the experimental results.

ISSN:1071-1023    

DOI:10.1116/1.584812

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

Large quantum‐confined Stark shift is observed in a type II GeSi/Si multiple quantum well structure for the first time. In this experiment, we have employed the photocurrent measurement using reverse biasedp‐i‐ndiodes with multiple quantum wells in thei‐region. The photocurrent as a function of bias is carried out at 77 and 300 K. The results show large red shift of the absorption edge which is about 0.75 meV kV−1 cm. This suggests the application of GeSi/Si type II structure for nonlinear electro‐optics devices near the 1.3 μm range.

ISSN:1071-1023    

DOI:10.1116/1.584813

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

Substrate‐stabilized, metastable, single‐crystal Ge1−xSnxfilms can be grown by molecular‐beam epitaxy (MBE). We have grown for the first time single crystal Ge1−xSnxalloys on lattice matched GaSb (withx=0.5) and InP (withx=0.26) substrates up to a thickness of 0.3 μm. Reflection high‐energy electron diffraction (RHEED) observations and x‐ray measurements show that even at very small lattice mismatch (less than 0.05%), single crystal Ge1−xSnxfilms cannot be grown thicker than 0.3 μm. Our x‐ray results suggest that the critical thickness of α‐Sn and Ge1−xSnxsingle crystal films is mainly determined by a phase transition mechanism, and the dislocation generation equivalent critical thickness is an overestimate. Under practical MBE growth conditions, it is very difficult to grow thick films, due to the sensitivity of the critical thickness to composition fluctuations. We have shown that even under an exact lattice match between substrate and film, the critical film thickness is limited.

ISSN:1071-1023    

DOI:10.1116/1.584814

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

The use of patterned Si substrates (specifically porous Si) for the reduction of heteroepitaxial film strain energy [S. Luryi and E. Suhir, Appl. Phys. Lett.49, 140 (1986)] has been studied recently by several research groups. We report experimental studies and discuss the validity of the original concept. We studied molecular beam epitaxial growth of continuous GexSi1−xfilm on 〈100〉 porous Si substrates using Rutherford backscattering spectrometry, transmission electron microscopy, and x‐ray rocking curves. The results show predominantly 60° dislocations with long misfit segments. There is no reduction in either strain in the films or dislocation density compared to the samples grown on regular Si substrates. In order to reduce defect densities, the stress fields from different growth areas of patterned substrate must not interfere. Arguments based on crystallographic considerations are presented which demonstrates that, first, the porous Si substrate is not suitable for such applications because of the nature of interconnected growth areas, and second, any kind of decaying stress field requires a certain degree of wafer warpage which does not always present in a realistic MBE‐grown heterostructure. It is the conclusion of this discussion that the strain energy in a continuous heteroepitaxial film grown on patterned substrates does not reach a limiting value, but continues to increase with the film thickness.

ISSN:1071-1023    

DOI:10.1116/1.584815

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

Scanning tunneling microscopy is used to investigate aspects of the initial stages of molecular‐beam epitaxy of Si on Si(001). A self‐diffusion coefficient is extracted. Anisotropic island shapes in the growth are attributed to an anisotropic lateral accommodation coefficient. Growth on vicinal surfaces shows that the barrier for atoms to cross a step cannot be much different from the barrier for migration on the terrace itself.

ISSN:1071-1023    

DOI:10.1116/1.584816

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

Steps on Si(111) surfaces are shown to be preserved at the interfaces of epitaxial silicide layers grown at room temperature. Symmetry requires the formation of a dislocation at every step of this (typeB) interface. This has enabled the examination, by transmission electron microscopy, of the topography of large areas of the Si surface after various treatments. Silicon molecular‐beam epitaxy (MBE) is shown to occur via step‐flow mechanism at high temperatures, and through nucleation and growth of islands on the terraces at low growth temperatures. These observations point to the importance of including nucleation mechanism into existing theories, especially at high supersaturation. A change of step character from 〈112̄〉to 〈∼(11) 2〉 at the initial stage of MBE is observed and is attributed to the stabilities of the two types of steps in relationship to the 7×7 structure. Preliminary results on vicinal Si(111) surfaces are also presented.

ISSN:1071-1023    

DOI:10.1116/1.584817

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

Ultrathin single crystal buried metal layers of NiAl have been grown within (Al,Ga)As heterostructures. The layers are electrically continuous down to 1 nm in thickness. Furthermore, property changes such as increased in‐plane electron–electron interactions, and vertical transport resonant tunneling behavior, attributed to the decreased dimensionality of such ultrathin layers, demonstrate that, in this regime, the films can be considered as metallic quantum wells. The resonant tunneling has been exploited in making a three‐terminal buried metallic well device. We discuss initial results of promising experiments aimed at decreasing the lattice mismatch between the metal and the semiconductor (1) by adding In to the GaAs and (2) by substituting the more closely lattice‐matched CoAl for NiAl.

ISSN:1071-1023    

DOI:10.1116/1.584818

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

In this paper, we report a new process for molecular beam epitaxial (MBE) GaAs‐on‐Si growth. The process involves high‐temperatureinsituGaAs annealing above 850 °C. The unique points in this new approach are: (1) the thermal cycling layers or so‐called thermal strained superlattices (TSL) are inserted in buffer growth and found to be effective in blocking dislocation propagation; (2) a thin Al0.35Ga0.65As cap layer is deposited after GaAs buffer layer growth to prevent the underneath GaAs epitaxial layer from sublimation during annealing. An 850 °CinsituAlGaAs cap annealing (ACA) of the AlGaAs/GaAs buffer layer can eliminate all the twins and stacking faults in the buffer layers and yield high‐quality GaAs film. The bulk GaAs overlayers is grown at normal GaAs/Si growth temperature and is never exposed to a high anneal temperature. High‐quality GaAs/Si layers with surface dislocation densities 1×106cm−2and an x‐ray linewidth of 130 arc s have been achieved.

ISSN:1071-1023    

DOI:10.1116/1.584820

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

An x‐ray study of annealing effects in Si0.65Ge0.35/Si strained‐layer superlattices grown by molecular‐beam epitaxy (MBE) at 500 °C is reported. The samples were subjected to thermal treatments between 600 and 698 °C, and the superlattice peaks and Si(004) peak were monitored at both low and high angles using powder and double crystal diffractometries. The interdiffusion coefficient of the average composition, obtained from the decay in intensity of the first superlattice peak about (000), was found to be similar to the results obtained from satellites about (004). This leads to the important conclusion that the diffusion coefficient can be obtained using the high‐angle technique, which is generally faster and less susceptible to experimental errors. The comparison between the two groups of measurements further emphasizes the fact that the critical slopes of the intensity plots should be excluded from the calculation of the diffusion coefficient.

ISSN:1071-1023    

DOI:10.1116/1.584821

出版商:American Vacuum Society    

年代:1990

数据来源: AIP