Peter Goodhew

Plastic relaxation and relaxed buffer layers for semiconductor epitaxy

We present a critical review of the strategies used in the fabrication of mismatched semiconductor heterostructures. By using simple concepts derived from the Matthews model of misfit relief, we show how the relaxation of single layers and complex structures may be analysed and predicted. These techniques allow a broad view of the processes that take place in the relaxation of strained layers. This is followed by a discussion of how the relative misfits and thicknesses of different layers in a heterostructure may influence the behaviour and distribution of dislocations in the structure. Finally, we describe the historical development and status of the experimental work and development that has been carried out in this area.

On the origin of misfit dislocations in InGaAs/GaAs strained layers

InxGa1−xAs/GaAs (x≤0.25) strained layers grown by molecular‐beam epitaxy have been examined by plan‐view transmission electron microscopy. Evidence is presented for the existence of two critical thicknesses, corresponding to the turnover of threading disloca‐ tions and the nucleation of new dislocations. From a quantitative analysis of dislocation intersections it is deduced that not all interfacial dislocations act to relieve the misfit strain.

Quantitative compositional analysis of InAs/GaAs quantum dots by scanning transmission electron microscopy

We present a quantitative technique for the direct compositional analysis of quantum dots (QDs), in which scanning transmission electron microscopy is applied to a capped InAs/GaAs QD layer in a structure also containing InxGa1−xAs/GaAs quantum well (QW) layers to provide an internal calibration of the In content. By obtaining energy dispersive x-ray analysis line scans through both QWs and QDs, the composition of the QDs can be determined by reference to the known composition of the QWs. In this article the method is described and demonstrated using two InAs/GaAs structures in which the QDs are nominally identical, but with different In composition in the calibration QW layers. We find that the QDs in both structures have an In composition of 65%–67% and the associated wetting layers contain approximately 12% In.

A study of surface cross-hatch and misfit dislocation structure in In0.15Ga0.85As/GaAs grown by chemical beam epitaxy

It is well known that a cross-hatch develops on the surface of low-misfit strained semiconductor layers which undergo relaxation by the introduction of arrays of a2〈101〉 misfit dislocations in the interface between the strained layer and substrate. Here we present a study of the detailed structure of these surface striations and their development with thickness in a series of InxGa1 − xAs single layers on (001) GaAs, where x is close to 0.15. Using atomic force microscopy, it is found that the striations are in fact almost triangular ridges with rounded tops separated by V-shaped grooves. They are not slip traces. These ridges are found to be asymmetric in distribution, with those parallel to [110] far higher than those parallel to [110]. The spacing and height of the ridges increases with layer thickness. The structure also becomes more disordered in the case of thicker layers, with ridges running for shorter lengths and having more complex profiles. Using transmission electron microscopy, it is possible to link the ridges to dislocations lying above, and parallel to, the interface which result from repeated operation of multiplication sources.

CBE growth of GaAs/GaAs, GaAs/Si and AlGaAs/GaAs using TEG, AsH3 and amine-alane precursors

The growth of high quality AlGaAs by CBE bas been limited by the high levels of carbon and oxygen contamination. The use of alane based precursors offers a significant reduction in such contamination. We report for the first time the CBE growth of AlxGa1-xAs from triethylgallium, dimethylethylamine-alane and arsine, and compare with. growth from triethylgallium, trimethylamine-alane and arsine. Some preliminary results of work on the CBE growth of GaAs on silicon will also be reported.

Comparison of the crystalline quality of step-graded and continuously graded InGaAs buffer layers

Abstract In this paper we summarize work carried out to investigate the relaxation of epitaxial strained layers of InGaAs on GaAs, where the InGaAs composition has been increased throughout the layer in either a stepwise or linearly graded form. The results are presented from the viewpoint of exploiting the relaxed layers to provide prescribed in-plane surface lattice parameters for subsequent use as “virtual” substrates for novel devices. We compare the behaviour of step-graded and linearly graded InGaAs layers. We consider the crystalline quality of different structures and discuss the design requirements for subsequent device quality growth.

Metal‐induced dislocation nucleation for metastable SiGe/Si

A new mechanism of misfit dislocation nucleation is demonstrated. Deliberate contamination with approximately 0.003 monolayers of Cu and subsequent annealing at 600 °C is shown by transmission electron microscopy, photoluminescence, and defect etching to produce dislocation half loops in a 1.1 μm layer of Si0.93Ge0.07 on a silicon substrate.

Direct measurement of composition of buried quantum dots using aberration-corrected scanning transmission electron microscopy

The authors present a direct method to quantitatively measure the indium composition of buried InAs quantum dots embedded in a GaAs matrix. In this method, spatially resolved electron-energy-loss spectroscopy combined with aberration-corrected scanning transmission electron microscopy at atomic resolution was employed to measure compositional profiles across the center of a quantum dot and the adjacent wetting layer. The size and shape of the quantum dots were determined using the Z contrast in high angle annular dark field images. A substantial enrichment in indium at the top of the quantum dots was identified, which is consistent with theoretical predictions.

Relaxation of InGaAs layers grown on (111)B GaAs

The relaxation behavior of InGaAs layers grown by molecular beam epitaxy on (111)B GaAs is investigated and compared with simultaneously grown (100) reference samples. Surface morphology, defect microstructure, and optical quality of the layers during the relaxation process are studied by Nomarski interference contrast, transmission electron microscopy, low‐temperature photoluminescence, and Raman spectroscopy. These techniques reveal an inhomogeneous and anisotropic relaxation in (111) samples. In (111) samples, the increase of critical thickness and the slower relaxation dependence on thickness, as compared with the (100) reference samples, is discussed

An approach to the systematic distortion correction in aberration corrected HAADF images

Systematic distortion has been analysed in high‐angle annular dark‐field (HAADF) images which may be caused by electrical interference. Strain mapping techniques have been applied to a strain‐free GaAs substrate in order to provide a broad analysis of the influence of this distortion on the determination of local strain in the heterostructure. We have developed a methodology for estimating the systematic distortion, and we correct the original images by using an algorithm that removes this systematic distortion.