Glide Of Threading Dislocations Research Articles

Glide of threading dislocations in (In)AlGaAs on Si induced by carrier recombination: Characteristics, mitigation, and filtering

III-V optoelectronics grown epitaxially on Si substrates have large networks of dislocations due to a lattice constant mismatch between the device layers and the substrate. Recombination-enhanced dislocation glide (REDG) allows these dislocations to move and increase in length during device operation, which degrades performance. In this paper, we study REDG dynamics of threading dislocations in situ in (In)AlGaAs double heterostructures grown on Si substrates using scanning electron microscopy cathodoluminescence. The driving force for REDG arises due to the coefficient of thermal expansion differences between Si and the III-V layers leading to large residual strains in the films. Tracking of threading dislocations as moving dark spot defects reveals glide characteristics that vary based on the nature of the dislocation. Remarkably, the alloying of a few atom percent of indium using metamorphic structures arrests threading dislocation glide by more than two orders of magnitude. Finally, we present REDG-based filtering as a pathway to reducing the threading dislocation density in select areas, removing a large fraction of the mobile dislocations. Together, these techniques will enable the understanding of dislocation–dislocation and carrier–dislocation interactions that have so far remained elusive during device operation, leading to reliable III-V integrated optoelectronics on silicon.

Epitaxial growth of tungsten layers on MgO(001)

Smooth single crystal W(001) layers were grown on MgO(001) substrates by magnetron sputtering at 900 °C. X-ray diffraction ω–2θ scans, ω-rocking curves, pole figures, and reciprocal space maps indicate a 45°-rotated epitaxial relationship: (001)W‖(001)MgO and [010]W‖[110]MgO, and a relaxed lattice constant of 3.167 ± 0.001 nm. A residual in-plane biaxial compressive strain is primarily attributed to differential thermal contraction after growth and decreases from −0.012 ± 0.001 to −0.001 ± 0.001 with increasing layer thickness d = 4.8–390 nm, suggesting relaxation during cooling by misfit dislocation growth through threading dislocation glide. The in-plane x-ray coherence length increases from 3.4 to 33.6 nm for d = 4.8–390 nm, while the out-of-plane x-ray coherence length is identical to the layer thickness for d ≤ 20 nm, but is smaller than d for d ≥ 49.7 nm, indicating local strain variations along the film growth direction. X-ray reflectivity analyses indicate that the root-mean-square surface roughness increases from 0.50 ± 0.05 to 0.95 ± 0.05 nm for d = 4.8–19.9 nm, suggesting a roughness exponent of 0.38, but remains relatively constant for d > 20 nm with a roughness of 1.00 ± 0.05 nm at d = 47.9 nm.

True green semipolar InGaN-based laser diodes beyond critical thickness limits using limited area epitaxy

Semipolar oriented laser diodes (LDs) have fundamental advantages over c-plane oriented LDs, however, the thickness and composition of InGaN waveguiding layers and AlGaN cladding are limited by the onset of stress relaxation via threading dislocation glide on the c-plane slip system. Limited area epitaxy minimizes misfit dislocation (MD) formation by preventing pre-existing TDs from entering a patterned mesa. We examine the effects of mesa height and facet evolution for LAE grown strained layers. Significant MD formation was suppressed by at least a factor of four for Al0.1Ga0.9N/GaN superlattices, enabling AlGaN-clad structures similar to those used in c-plane LDs. We then demonstrate AlGaN-clad blue (456 nm) LDs with threshold current density (Jth) of 4.5 kA/cm2 and GaN-clad true green (523 nm) LDs with Jth of 12 kA/cm2. TEM measurements of the green LD confirm reduction of MD densities with reduction of MD run length. LAE is effective for improving the optical confinement factor of semipolar LDs and offers a glimpse of the design space that may soon be available using low TD density bulk GaN substrates.

Misfit dislocation formation at heterointerfaces in (Al,In)GaN heteroepitaxial layers grown on semipolar free-standing GaN substrates

Semipolar GaN-based light emitting devices show great promise because of reduced polarization-related electric fields in the quantum wells and the potential for high indium uptake in InxGa1−xN quantum wells. In semipolar GaN, the (0001) slip plane is inclined with respect to the film normal, thus shear stresses are present on this plane for nominally misfitting layer growth. We present scattering contrast transmission electron microscopy studies of (112¯2) and (202¯1) semipolar GaN-based laser diode structures. Misfit dislocations were observed at the nominally misfitting heterointerfaces in the (112¯2) structures with line direction [11¯00] and Burgers vector in the (0001) plane. Similar observations are reported for the (202¯1) structures. Overall, the results are consistent with stress relaxation by threading dislocation glide.

Fabrication of high quality Ge virtual substrates by selective epitaxial growth in shallow trench isolated Si (001) trenches

To further boost the CMOS device performance, Ge has been successfully integrated on shallow trench isolated Si substrates for pMOSFET fabrication. However, the high threading dislocation densities (TDDs) in epitaxial Ge layers on Si cause mobility degradation and increase in junction leakage. In this work, we studied the fabrication of Ge virtual substrates with low TDDs by Ge selective growth and high temperature anneal followed by chemical mechanical polishing (CMP). With this approach, the TDDs in both submicron and wider trenches were simultaneously reduced below 1 × 10 7 cm − 2 for 300 nm thick Ge layers. The resulting surface root-mean-square (RMS) roughness is about 0.15 nm. This fabrication scheme provides high quality Ge virtual substrates for pMOSFET devices as well as for III–V selective epitaxial growth in nMOSFET areas. A confined dislocation network was observed at about 50 nm above the Ge/Si interface. This dislocation network was generated as a result of effective threading dislocation glide and annihilation. The separation between the confined threading dislocations was found in the order of 100 nm.

Heterostructures Ge xSi 1−x/Si(0 0 1) grown by low-temperature (300–400 °C) molecular beam epitaxy: Misfit dislocation propagation

In previous publications [ Tuppen and Gibbings, J. Appl. Phys. 68 (1990) 1526; Hull et al., J. Appl. Phys. 70 (1991) 2052; Houghton, J. Appl. Phys. 70 (1991) 2136], the glide velocity of dislocations was analyzed and estimated in GeSi/Si (0 0 1) heterostructures grown at a temperature of 550 °C. The method of growing GeSi films with the use of a low-temperature Si buffer has been developed recently and was not involved in these studies. The present work deals with a more detailed analysis of dislocation propagation velocities in GeSi films grown with the use of the low-temperature Si buffer and those grown at low-temperatures. The dislocation velocity is estimated by the measuring of the length of misfit dislocations observed in annealed films. Additionally a method for estimating the mean threading dislocation glide velocity is used, which involves the measured threading dislocation density in a particular film and degree of its plastic relaxation directly related to the number of threading dislocations and their glide velocity. It is shown that dislocation glide velocities in heterostructures grown with the use of the low-temperature Si buffer and at low-temperatures are higher than the values predicted by the classical calculations by an order of magnitude.

Modeling crosshatch surface morphology in growing mismatched layers. Part II: Periodic boundary conditions and dislocation groups

We present further developments and understanding of the commonly observed crosshatch surface morphology in strain-relaxed heteroepitaxial films. We have previously proposed that the crosshatch morphology is directly related with strain relaxation via threading dislocation glide which results in both surface step and misfit dislocation (MD) formation [see Andrews et al., J. Appl. Phys. 91, 1933 (2002)—now referred to as Part I]. In this article, we have used solutions for the stress fields and displacement fields for periodic MD arrays which include the effects of the free surface. These solutions avoid truncation errors associated with finite dislocation arrays that were used in Part I. We have calculated the surface height profile for relaxed films where the misfit dislocations were introduced randomly or the misfit dislocations were placed in groups with alternating sign of the normal component of their Burgers vector. We have calculated the surface height profiles where the slip step remains at the surface [“slip step only” (SSO)] and where the slip step is eliminated [“slip step eliminated” (SSE)] due to annihilation of opposite sense steps, such as could happen during growth or lateral mass transport. For relaxed films, we find that the surface height undulations, characteristic of crosshatch, increase with increasing film thickness for the SSO case, whereas the surface becomes flatter for the SSE case. Experiments on relaxed In0.25Ga0.75As films on (001) GaAs show that the surface height undulations in the [110] direction increase with increasing film thickness. Thus, we conclude that with increasing film thickness the crosshatch in the slow diffusion [110] direction is best described by the SSO case.

Investigation of threading dislocation blocking in strained-layer InGaAs/GaAs heterostructures using scanning cathodoluminescence microscopy

Threading dislocation glide relieves strain in strained-layer heterostructures by increasing the total length of interface misfit dislocations. The blocking theory proposed by Freund [J. Appl. Phys. 68, 2073 (1990)] predicts the thickness above which gliding threading dislocations are able to overcome the resistance force produced by existing orthogonal misfit dislocations. A set of wedge-shaped samples of InxGa1−xAs/GaAs (x=0.04) strained-layer heterostructures was grown using molecular-beam epitaxy in order to test the theory of dislocation blocking over a range of thicknesses within one sample. Scanning cathodoluminescence microscopy techniques were used to image the misfit dislocations. The cathodoluminescence results confirm the model proposed by Freund.