Heteroepitaxial Lateral Overgrowth Research Articles

Stress engineering of high-quality single crystal diamond by heteroepitaxial lateral overgrowth

A method for lateral overgrowth of low-stress single crystal diamond by chemical vapor deposition (CVD) is described. The process is initiated by deposition of a thin (550 nm) (001) diamond layer on Ir-buffered a-plane sapphire. The diamond is partially masked by periodic thermally evaporated Au stripes using photolithography. Lateral overgrowth of the Au occurs with extremely effective filtering of threading dislocations. Thermal stress resulting from mismatch of the low thermal expansion diamond and the sapphire substrate is largely accommodated by the ductile Au layer. The stress state of the diamond is investigated by Raman spectroscopy for two thicknesses: at 10 μm where the film has just overgrown the Au mask and at 180 μm where the film thickness greatly exceeds the scale of the masking. For the 10-μm film, the Raman linewidth shows spatial oscillations with the period of the Au stripes with a factor of 2 to 3 reduction relative to the unmasked region. In a 180-μm thick diamond film, the overall su...

Diamond Heteroepitaxial Lateral Overgrowth

ABSTRACTA method of diamond heteroepitaxial lateral overgrowth is demonstrated which utilizes a photolithographic metal mask to pattern a thin (001) epitaxial diamond surface. Significant structural improvement was found, with a threading dislocation density reduced by two orders of magnitude at the top surface of a thick overgrown diamond layer. In the initial stage of overgrowth, a reduction of diamond Raman linewidth in the overgrown area was also realized. Thermally-induced stress and internal stress were determined by Raman spectroscopy of adhering and delaminated diamond films. The internal stress is found to decrease as sample thickness increases.

Germanium on Insulator (GOI) Structure Using Hetero-Epitaxial Lateral Overgrowth on Silicon

A technique to achieve germanium on insulator (GOI) structure on Si platform using hetero-epitaxial lateral overgrowth is presented. On (100) Si wafer, SiO2 is thermally grown, and patterned to locally reveal Si surface on which Ge is grown via selective epitaxy. After filling the growth window, Ge starts growing laterally, and adjacent Ge crystals coalesce with each other on SiO2. After the coalescence, <100> directional growth is made dominant, to fill the valley and planarize the surface. Thus, single crystalline Ge film sitting on SiO2 can be made for GOI applications.

Chemical Lift-Off of Blue Light-Emitting Diodes Grown on Sapphire Substrate with an Oxide-Patterned Sacrificial Layer

A high quality GaN epilayer was successfully grown on a sapphire substrate with patterned SiO2 as a sacrificial structure utilizing the direct heteroepitaxial lateral overgrowth method. The light-emitting diode (LED) structure was subsequently grown on the GaN epilayer and fabricated using a chemical lift-off process. After SiO2 was removed with a HF solution, the LEDs with Cu substrate could be separated from the sapphire substrate due to an increase in the GaN/sapphire interfacial strain. Similar forward voltage and output power characteristics were obtained for vertical LEDs fabricated using chemical lift-off and laser lift-off processes.

Efficiency Improvement of GaN-Based LEDs With $ \hbox{SiO}_{2}$ Microrod Array and Textured Sidewalls

High-performance nitride-based light-emitting diodes (LEDs) grown with SiO2 microrod array have been demonstrated. The light output power of LEDs with SiO2 microrod array was 9.03% higher than conventional LEDs at the injection current of 20 mA. The improvement contributed to the enhancement of the light extraction efficiency, and epitaxial GaN film quality improved by direct heteroepitaxial lateral overgrowth with SiO2 microrod array. The light output power could be further enhanced by about 18.36% as compared with the conventional LEDs when adopting the textured sidewall surface which use buffered oxide etch to remove SiO2 microrod arrays and use NaOH to etch the sidewall again into an inverted pyramid shape. After the texturing process, the LEDs show higher electroluminescence intensity and broader far-field pattern. Furthermore, the LEDs with SiO2 microrod array and additional wet-etching process will not affect the electrical property.

Fabrication of GaN‐based light emitting diodes using direct heteroepitaxial lateral overgrowth on patterned sapphire substrates with thick SiO2 masks

AbstractWe have successfully obtained high‐quality GaN films directly on thick SiO2 patterned sapphire substrates by utilizing modified facet‐controlled epitaxial lateral overgrowth (FACELO). GaN films were grown by metalorganic vapour phase epitaxy on the stripe patterned substrates with the SiO2 thickness of 1.2 μm. The threading dislocation density reached a value as low as 5 × 107 cm–2. We have also fabricated Light emitting diodes (LEDs). The output power and external quantum efficiency of the LED operated at 20 mA were 20.74 mW and 37.1%, respectively. This is due to not only the reduced dislocation density but also the improved light extraction efficiency because of the light scattering at the patterned GaN/thick‐SiO2‐masks interface. (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

UV laser diode with 350.9-nm-lasing wavelength grown by hetero-epitaxial-lateral overgrowth technology

We have demonstrated a UV-laser diode with a lasing wavelength of 350.9 nm, which has a GaN-AlGaN multiquantum-well (MQW) active layer and was grown on low-dislocation-density Al/sub 0.18/Ga/sub 0.82/N template. The Al/sub 0.18/Ga/sub 0.82/N template was produced by the hetero-epitaxial lateral overgrowth technology on the low-cost sapphire substrate, and has partially low-dislocation density of approximately 2/spl times/10/sup 7/ cm/sup -2/. The lasing operation under pulsed current injection was achieved with the threshold current density of 7.3 kA/cm/sup 2/ and the operating voltage of 10.4 V.

Direct heteroepitaxial lateral overgrowth of GaN on stripe-patterned sapphire substrates with very thin SiO2 masks

Direct heteroeptaxial lateral overgrowth of GaN was performed on sapphire substrates by low-pressure metalorganic chemical vapor deposition. The substrates were patterned with very thin SiO2 stripes with the thickness of 200∼300 Å. The growth was carried out by a two-step condition. In the first step for facet-controlled epitaxy, the formation of a triangular cross-section of GaN stripes grown directly on the patterned sapphire was achieved to terminate threading dislocations (TDs) in the opening regions on the inclined {11–22} facets. During the second step for lateral growth, the TDs were bended completely by strong lateral overgrowth. The densities of the step terminations in atomic force microscopic images, corresponding screw- or mixed-type TDs were effectively reduced to less than 107 cm–2 over the entire region. The crystallographic tilt between the mask and the opening regions was also well suppressed by using the very thin SiO2 mask as thick as GaN nucleation layer. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

UV Light-Emitting Diode Fabricated on Hetero-ELO-Grown Al0.22Ga0.78N with Low Dislocation Density

Using a hetero-epitaxial lateral overgrowth (ELO) technology with low-temperature deposited AlN interlayer, high-quality crack-free Al 0.22 Ga 0.78 N with low dislocation density is realized. The dislocation density in the Al 0.22 Ga 0.78 N was reduced to as low as the order of 10 7 cm -2 over the whole wafer. Applying the high-quality AlGaN layer to a UV light-emitting diode (LED), high output power of more than 0.1 mW at a forward current of 50 mA has been demonstrated with the emission peak wavelengths from 323 to 352 nm. The highest output power of 0.6 mW is obtained for the 352 nm LED with GaN/AlGaN multiple quantum well active layer. The emission efficiency was dependent on the wavelength, and the 323 nm LED has the lowest output power of 0.18 mW at 50 mA bias. One of the factors determining the external quantum efficiency is thought to be an inferior hole spread in highly resistive p-type layers.

Reduction of threading dislocation density in Al XGa 1− XN grown on periodically grooved substrates

We proposed a heteroepitaxial lateral overgrowth technique using periodically grooved substrates to prepare a GaN single crystal with low dislocation density. By this technique, GaN single crystals have been grown without a selective growth mask or GaN single crystal seeds. Moreover, the AlGaN single crystal, which is important for optoelectronic devices in the UV region, can also be grown using this technique. The reduction of the threading dislocation density in Al X Ga 1− X N single crystals grown on periodically grooved substrates was confirmed by transmission electron microscopy.

Low-dislocation-density GaN and Al xGa 1− xN ( x⩽0.13) grown on grooved substrates

We proposed the heteroepitaxial lateral overgrowth technique using grooved sapphire (0 0 0 1) and (1 1 2 ̄ 0) SiC(0 0 0 1) Si and Si(1 1 1) substrates to prepare Al x Ga 1− x N single crystalline films with low dislocation density. Straight grooves of these substrates were aligned parallel to the 〈1 1 ̄ 0 0〉 or 〈1 1 2 ̄ 0〉 direction of Al x Ga 1− x N. In this technique, neither a selective growth mask nor patterned GaN single crystal film was used. Dislocation densities lower than about 10 6 cm −2 were ascertained via plan-view TEM. This technique is promising for growing low-dislocation-density nitride-based semiconductors.

Cathodoluminescence from relaxed Ge xSi 1− x grown by heteroepitaxial lateral overgrowth

We present low temperature cathodoluminescence (CL) studies of relaxed Ge x Si 1− x , selectively grown on a patterned Si (111) substrate by liquid phase epitaxy, using heteroepitaxial lateral overgrowth. In the spectrally resolved CL of the resulting GeSi crystals, we observe an emission peak attributed to the recombination of free excitons (FEs). We further observe a peak of lower intensity at a lower energy position, caused by the unresolved phonon replicas of the FE peak. At an even lower energy position, we observe a comparatively broad luminescence band, attributed to CL from dislocations. Monochromatic images using the FE emission, or its phonon replica, reveal three types of contrast variations. On a 5 μm scale we observe dark line defects in the GeSi crystals, which we attribute to dislocations. In the lateral position of the seeding windows for the epitaxy, the GeSi crystals exhibit a dark, 20 μm wide band. On a 20 to 50 μm scale we observe small fluctuations in the Ge x Si 1− x composition, which manifests itself as local intensity variations with detection wavelength.

Transmission electron microscopy characterization of InxGa1−xAs substrates grown by heteroepitaxial lateral overgrowth

InxGa1−xAs (x=0.04) ingots have been grown by liquid phase electroepitaxy (LPEE) on GaAs (001) substrates covered with a 0.2 μm thick SiO2 layer using a heteroepitaxial lateral overgrowth technique. Growth begins in 10 μm wide oxide-free seeding windows oriented at approximately 30° to the {110} planes of the substrate, and proceeds laterally over adjacent 90 μm wide oxide strips. Transmission electron microscopy (TEM) analysis of the resulting material reveals a decrease in dislocation densities in the alloy layer, as dislocation nucleation occurs only at the seeding windows, while growth proceeds defect-free over the oxide. Etching the seeding windows slightly into the substrate results in an increase in dislocation propagation into the substrate and under the oxide layer, and a lower dislocation density in the overlayer. The combination of the lateral overgrowth technique and the deeper window etching results in a significantly lower defect density in the InxGa1−xAs overlayer.

Heteroepitaxial lateral overgrowth of Ge xSi 1− x over SiO 2/Si structures by liquid phase epitaxy

We investigate heteroepitaxial lateral overgrowth (HELO) of Ge x Si 1− x and Ge over thermally oxidized Si. The Ge x Si 1− x lamellae are grown by liquid phase epitaxy and are exclusively bound by {111} faces. The growth parameters which govern the shape, overgrowth width w and thickness h of the HELO Ge x Si 1− x and Ge lamellae are presented. Heteroepitaxial lateral overgrowth is found to take place in all crystallographic directions on the (111) plane. The lateral overgrowth width w is quantitatively described as a function of seeding window orientation. Seeding windows parallel to <112> directions yield maximum overgrowth widths w up to 140 μm and lateral-to-vertical growth width aspect ratios w/h up to 11:1 under our chosen experimental conditions. The HELO Ge x Si 1− x lamellae have a smoother surface morphology compared to Ge x Si 1− x grown on unmasked Si.