Influence of substrate misorientation on the structural quality of lattice matched GaAs/ScYbAs/GaAs structures (original) (raw)
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2013
Structural, morphological, and band offset properties of GaAs/Ge/GaAs heterostructures grown in situ on (100), (110), and (111)A GaAs substrates using two separate molecular beam epitaxy chambers, connected via vacuum transfer chamber, were investigated. Reflection high energy electron diffraction (RHEED) studies in all cases exhibited a streaky reconstructed surface pattern for Ge. Sharp RHEED patterns from the surface of GaAs on epitaxial Ge/(111)A GaAs and Ge/(110)GaAs demonstrated a superior interface quality than on Ge/(100)GaAs. Atomic force microscopy reveals smooth and uniform morphology with surface roughness of Ge about 0.2-0.3 nm. High-resolution triple axis x-ray rocking curves demonstrate a high-quality Ge epitaxial layer as well as GaAs/Ge/GaAs heterostructures by observing Pendell€ osung oscillations. Valence band offset, DE v , have been derived from x-ray photoelectron spectroscopy (XPS) data on GaAs/Ge/GaAs interfaces for three crystallographic orientations. The DE v values for epitaxial GaAs layers grown on Ge and Ge layers grown on (100), (110), and (111)A GaAs substrates are 0.23, 0.26, 0.31 eV (upper GaAs/Ge interface) and 0.42, 0.57, 0.61 eV (bottom Ge/GaAs interface), respectively. Using XPS data obtained from these heterostructures, variations in band discontinuities related to the crystallographic orientation have been observed and established a band offset relation of DE V ð111ÞGa > DE V ð110Þ > DE V ð100ÞAs in both upper and lower interfaces. V
Microstructural differences of the two possible orientations of GaAs on vicinal (001) Si substrates
Journal of Crystal Growth, 2001
Two alternative orientations of a GaAs layer in respect to a vicinal (0 0 1) substrate, misoriented toward [1 1 0], are possible for most of the miscut angles; type A orientation having the GaAs [1 1 0] parallel to the [1 1 0] Si misorientation direction and type B with the GaAs [1 1 0] parallel to the [1 1 0] Si direction. The dependence of the GaAs surface roughness and of the tilting between the GaAs and Si (0 0 1) planes on the GaAs/Si orientation and the miscut angle of the vicinal substrate, in the range of 0-98, has been investigated. The GaAs/Si surface roughness was characteristic for preferential growth along [1 1 0]. Thin GaAs films of approximately 2 mm thickness exhibited an almost constant rms roughness of 6.5-7.0 nm for the type A orientation, while the rms roughness varied in the range of 4.2-60 nm for the type B orientation, depending on the value of the miscut angle. The tilting angle between the GaAs and Si (0 0 1) planes exhibited different signs for the two types of orientation and much higher values for the type B orientation. A rather constant negative tilting was observed for type A samples, in the range of miscut angles of 1.5-7.58. The results suggest that the GaAs/Si lattice tilting may be a sensitive index for the domain purity in the GaAs/Si films. #
Surface structure of GaAs(2 5 11)
Physical Review B, 2002
GaAs samples with orientations vicinal to ͑2 5 11͒ within 1°were prepared by molecular beam epitaxy and analyzed in situ by scanning tunneling microscopy, low-energy electron diffraction, and reflection high-energy electron diffraction. In addition, first-principles electronic structure calculations were carried out. GaAs͑2 5 11͒ is a stable surface whose orientation is located within the stereographic triangle. For a wide range of As-rich conditions a (1ϫ1) reconstruction forms that is characterized by an inclined series of three As dimers and that fulfills the electron counting rule. The terrace size is limited only by the macroscopic off-orientation of the samples. The surface is perturbed by thin stripes of the nearby orientation ͑3 7 15͒. While the dangling bond densities of GaAs͑2 5 11͒ and GaAs͑3 7 15͒ are almost equal, GaAs͑3 7 15͒ violates the electron counting rule. The analysis of this perturbation suggests that, in general, on semiconductor surfaces the gain in stability arising from the minimization of the number of dangling bonds is significantly greater than the gain arising from reaching a semiconducting ground state. Upon annealing of the samples in ultrahigh vacuum, a fairly rough surface structure develops whose mean orientation is different from ͑2 5 11͒.
MBE growth of lattice-matched and mismatched films on non-(001) GaAs substrates
Thin Solid Films, 1997
There has recently been great interest in growth by molecular beam epitaxy of GaAs films on non-(001) oriented GaAs substrates. This has occurred largely because of the possibility of fabricating novel device structures such as quantum wires and quantum boxes using patterned substrates. However, the growth of high quality lattice matched and mismatched structures on non-(0011 GaAs substrates has had a reputation amongst many researchers of being 'difficult'. Epitaxial layers grown on these surfaces have generally had poor surface morphology, bad crystalline quality and irreproducible dopant incorporation behaviour. In this paper we will show that the growth of these materials is not 'difficult', but 'different' and that provided suitable growth conditions are used then high quality layers may be deposited on all substrate orientations. As an illustration we will use reflection high energy electron diffraction to predict the conditions for high quality growth GaAs on the GaAs(l1 IIA. We will then extend this to the mismatched (InGa)As:GaAs(l 11)A system. 0 1997 Elsevier Science S.A.
Thin Solid Films, 1999
The dependence of the detct structure on substrate misorienration is investigated in InGaAs/GaAs(I I I) multiple quanrum well hetrerostructures. Samples were simultaneously grown by molecular beam epitaxy on GaAs(I I I!B subhtrateb mkoricntrd I' off towards [?I 11 and 1' off towards [Iii] under optimized growth conditions for both otf-dxis sub5trarrb. For both .\ubbtrdle misorientutions wo different dislocation networks are evidenced: first. a triangular 60" misfit disiocarion array with (iiOj directions and second. a new dislocation conliguration seen for the first time with diJocation lines parallels to (,I I?j directions. This lawr can work as a dislocation multiplication source t'or In-content above 25% for the strucw-e chosen being more active in 2" OK subbtrattb than in 1' off web. The xrivuiion of rhib ne\v dislocation source may drastically affect the optical properties ol' the multiple quantum wells.
The morphology of high-index GaAs surfaces
Applied Surface Science, 2000
Ž. Ž. Ž. In this contribution, an overview of the research work in our group on the GaAs 112 , 113 and 114 surfaces is Ž. presented. Samples were prepared by molecular beam epitaxy MBE and analyzed in situ by low-energy electron diffraction Ž. Ž. Ž. LEED , core level spectroscopy and scanning tunneling microscopy STM. The GaAs 112 A surface is unstable and Ä 4 Ž. Ä 4 decomposes into five facets of the orientations 110 , 111 and 124. Real space images reveal that the facets form Ž. depressions whose horizontal cross-section is an irregular pentagon. For the GaAs 113 A surface, our results support the Ž. Ž. Ž. 8 = 1 reconstruction proposed by Wassermeier et al. On the GaAs 114 A surface a c 2 = 2 reconstruction was found. A Ž. Ž. structure model based on the GaAs 001-2 = 4 a reconstruction is in agreement with all our results.
GaAs peculiarities related with inhomogeneities and the methods for reveal of their properties
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2001
The inhomogeneities in as-grown and irradiated GaAs crystals and structures, their properties and role have been analysed. The influence of inhomogeneities on the properties of crystal and Schottky diode structure are presented. The possibilities of different methods for material and structure characterisation (Hall effect and magnetoresistance, noise spectra, thermally stimulated current and polarisation, photoconductivity kinetics and spectrum, light-induced diffraction) are discussed.
Acta Physica Polonica A, 1993
The defect patterns in GaAs crystal grown using liquid encapsulated Czochralski and gradient freeze methods with various types of doping were characterized using complementary X-ray topographic methods. It was found that the cellular structure occurring in the 1ow doped crystal is developed independently from the actual growth surface. The occurrence of the cellular structure is connected with significant 1attice deformation, and some results point that significant stress can influence its formation. The high doping prevents formation of the cellular structure, but at higher doping the phenomenon of "cellular growth" can occur due to instabilities of the growth surface. The present results point that defect pattern in GaAs crystals is more affected by the type of doping than by the choice of the growth method.