Strain profiles in overcritical (001) ZnSe/GaAs heteroepitaxial layers

High-resolution X-ray diffraction at variable temperatures was used to study the strain state in ZnSe layers of different thicknesses grown on GaAs(001) substrates and of GaN layers deposited on sapphire. In the ZnSe layers, a biaxial compressive strain component due to the lattice mismatch and a biaxial tensile strain due to the different thermal expansion coefficients are superposed which in general can be well modelled. However, the assumptions of the model may be violated for partially relaxed layers. A residual lattice misfit induced strain is present in ZnSe layers as thick as 5.4 mm. On the contrary, the strain state in GaN layers is given by a superposition of biaxial thermally induced strain and hydrostatic strain, presumably induced by impurity incorporation.Introduction Thermally induced strains in thin films are of large significance for both common II±VI and III±N epitaxial layers. High-resolution X-ray diffraction (HRXRD) at variable temperatures provides the unique possibility to study directly the thermal strain in epitaxial layers. This is demonstrated in this work for the example of ZnSe layers of different thicknesses grown on GaAs(001) substrates and for GaN layers deposited on sapphire. The ZnSe/GaAs system is characterized by a lattice mismatch of 0.27% and a mismatch in thermal expansion coefficients (TEC) of 24% (both at room temperature) as well as by relatively low growth temperatures in molecular beam epitaxy (MBE) of about 300 C. On the contrary, GaN layers grown on c-plane sapphire have a similar thermal mismatch of À28% [1], but their lattice mismatch of 14% and their typical growth temperatures in MBE and metalorganic chemical vapour deposition (MOCVD) of 700 to 1100 C are much higher than for ZnSe layers.The relatively low lattice mismatch between ZnSe and GaAs results in a superposition of biaxial strain components due to the misfit of lattice constants and TEC values [2,3]. To study this superposition requires to vary the layer thicknesses or/and the measurement temperature. While often only the out-of-plane lattice parameter is studied [2 to 4], we analyze the in-plane mismatch as well enabling to verify directly the validity of theoretical models. On the contrary, the layer strain correlated with the huge lattice mismatch between GaN and sapphire should be relaxed after a few monolayers. However, GaN is known to often contain a remarkable hydrostatic strain due to impurity incorporation [5,6], which has to be taken into account to describe the strain situation in GaN layers correctly. Also in this case the in-plane lattice parameters have to be determined to separate both effects.

show abstract

“…Note that even the 5.4 mm thick ZnSe layer contains a residual compressive strain at its growth temperature of 550 K in agreement with Ref. [9].…”

Section: Resultssupporting

confidence: 89%

“…Figure 3c shows also the nonzero residual compressive strain present in the 5.4 mm thick ZnSe layer at growth temperature of 550 K in agreement with Ref. [9]. Thus, the direct interpretation of strains in several mm thick ZnSe layers as purely thermally induced seems to be at least doubtful.…”

Section: Resultssupporting

confidence: 84%

Thermally Induced Strain in ZnSe and GaN Epitaxial Layers Studied by High-Resolution X-Ray Diffraction at Variable Temperatures

Heinke

Haase

Grossmann

et al. 2000

phys. stat. sol. (a)

View full text Add to dashboard Cite

show abstract

“…However, RHEED yields no information about the vertical lattice constant a Ќ , which yields strain due to lattice mismatch and differences in thermal expansion. 4 Strain must be controlled, for example, in order to achieve shifts of electronic band gaps 5 or to induce the formation of self-organized quantum dots, 6 but in many cases strain will be disadvantageous, because it gives rise to the formation of lattice defects upon relaxation, which deteriorate the optical 7,8 and transport 9 properties. Up to now, strain is measured ex situ by x-ray diffraction ͑XRD͒.…”

mentioning

confidence: 99%

Real-time in situ x-ray diffraction as a method to control epitaxial growth

Bader

Faschinger

Schumacher

et al. 2003

Applied Physics Letters

View full text Add to dashboard Cite

We developed a real-time in situ x-ray Bragg diffraction technique for monitoring epitaxial growth. In our setup, the x-ray diffraction requirement of an extremely exact sample adjustment and an angular scan of sample and detector are circumvented by using a slightly divergent x-ray beam and observing an extremely asymmetric Bragg reflection with a multichannel detector. The angular range covered by the stationary multichannel detector corresponds nearly exactly to the qz interval of a conventional ω−2θ scan. The technique is demonstrated by monitoring the molecular-beam epitaxial growth of a ZnSe epilayer on (001)GaAs. The exposure time of each diffraction pattern is only a few seconds, which enables a real-time x-ray diffraction monitoring of the epitaxial growth process.

show abstract

“…These strains are relaxed by formation of structural defects like stacking faults and dislocations. Existing stacking faults and other defects near the interface, like the case of ZnSe grown on GaAs [1][2][3][4][5][6][7] are frequently the sources of new dislocations which propagate from the interface into the epitaxial epilayer [19] sometimes leading to internal micro-cracks.…”

Section: Properties Of the Samples After Pressure Treatmentmentioning

confidence: 99%

“…Several reports on ZnSe-based heterostructures have shown that formation of structural defects at the ZnSe/GaAs interface plays a crucial role in the degradation process [1][2][3][4][5][6][7]. Strains induced by the lattice mismatch between the substrate and the epilayer lead to creation of many crystal defects (point defects, dislocations, V-shape stacking faults etc) near the interface.…”

Section: Introductionmentioning

confidence: 99%

Effect of hydrostatic pressure on degradation of CdTe/CdMgTe heterostructures grown by molecular beam epitaxy on GaAs substrates

Wasik

Baj

Siwiec-Matuszyk

et al. 2001

Journal of Applied Physics

View full text Add to dashboard Cite

We have shown that external hydrostatic pressure leads to the creation of structural defects, mainly in the vicinity of the II-VI/GaAs interface in the CdTe/Cd 1-x Mg x Te heterostructures grown by the molecular beam epitaxy method on GaAs substrates.These defects propagating across the epilayer cause permanent damage to the samples from the point of view of their electrical properties. In contrast, photoluminescence spectra are only weakly influenced by pressure. Our results shed light on the degradation process observed even without pressure in II-VI -based heterostructures.2

show abstract

Strain profiles in overcritical (001) ZnSe/GaAs heteroepitaxial layers

Cited by 22 publications

References 22 publications

Thermally Induced Strain in ZnSe and GaN Epitaxial Layers Studied by High-Resolution X-Ray Diffraction at Variable Temperatures

Thermally Induced Strain in ZnSe and GaN Epitaxial Layers Studied by High-Resolution X-Ray Diffraction at Variable Temperatures

Real-time in situ x-ray diffraction as a method to control epitaxial growth

Effect of hydrostatic pressure on degradation of CdTe/CdMgTe heterostructures grown by molecular beam epitaxy on GaAs substrates

Contact Info

Product

Resources

About