Substrate Misorientation Research Articles

Influence of the a-directed off-cut on the opto-electrical properties of laser diodes grown on the 0.3° misoriented m-directed GaN substrate

We report on the results of the investigation of the influence of an additional a-directed off-cut of the substrate on the opto-electrical properties of the laser diodes grown on bulk GaN with initial misorientation 0.3° towards the m-direction. The investigated a-directed off-cut is varied from 0° up to 1° by means of multilevel laser lithography and dry etching. The results show that the increase of the a-directed off-cut causes the decrease of internal optical losses and increase of injection efficiency. In consequence, the devices fabricated on the wafer areas characterized by higher a-directed off cut are characterized by the lower threshold current, and higher slope and wall-plug efficiencies.

Effect of substrate crystalline orientation on boron-doped homoepitaxial diamond growth

Boron-doped diamond layers have been grown by MW PECVD on substrates with a misorientation over the range of 0 to 90° relative to the (100) crystalline plane while keeping all other growth conditions constant. Deposited layers were characterized by scanning electron microscopy, atomic force microscopy, and Raman spectroscopy. The deposition rate, surface roughness, and boron incorporation vary according to the substrate misorientation. These results show the essential need for rigorous control of the substrate crystalline orientation in the synthesis of doped diamond for electronic applications. Thick, smooth, and free of surface defects boron-doped epitaxial diamond layers were obtained over a broad range of crystalline orientations at high growth rates and high boron incorporation efficiency. Novelty statementThis work reports on the effect of the substrate crystalline orientation on the morphology, growth rate, and boron incorporation in epitaxial diamond layers deposited by plasma-enhanced chemical vapor deposition.

Flat Metamorphic Inalas Buffer Layer on Gaas(111)A Misoriented Substrates by Growth Kinetics Control

Flat Metamorphic Inalas Buffer Layer on Gaas(111)A Misoriented Substrates by Growth Kinetics Control

Effect of substrate misorientation on the properties of p-HEMT GaAs-based nanoheterostructures formed during MOCVD epitaxy

As one of the approaches to improve p-HEMT, we studied the effect of misorientation of GaAs substrates on the surface morphology, structure, and electrical properties of pseudomorphic heterostructures, as well as the parameters of transistors based on them. In a single technological cycle, heterostructures were formed on vicinal substrates with (100) orientation and misoriented by 2o to (110) by the method of MOCVD (MOCVD) in a single technological cycle. It has been established that on misoriented substrates, the growth of structurally consistent and stressed epitaxial layers occurs according to a layered-step mechanism with the formation of macrosteps. On vicinal substrates, the formation of monatomic growth steps was observed. The comparative characteristics of p-HEMT obtained using two types of substrates are considered. Keywords: GaAs/InGaAs/GaAlAs heterostructures, MOCVD epitaxy, p-HEMT, substrate misorientation, comparative characteristics of structures and p-HEMT based on them.

Improvements in Characteristics of N-Polar Si-Doped Algan Epi-Layer Grown on Mis-Oriented C-Plane Sapphire Substrate

Improvements in Characteristics of N-Polar Si-Doped Algan Epi-Layer Grown on Mis-Oriented C-Plane Sapphire Substrate

Improvements in Characteristics of N-Polar Si-Doped Algan Epi-Layer Grown on Mis-Oriented C-Plane Sapphire Substrate

Improvements in Characteristics of N-Polar Si-Doped Algan Epi-Layer Grown on Mis-Oriented C-Plane Sapphire Substrate

Structural and emission improvement of cyan-emitting InGaN quantum wells by introducing a large substrate misorientation angle

Within this work, we studied InGaN QWs with nominally 17% InN mole fraction grown within an 80 × 80 μm area with local misorientation angle change from 0.3° to 3.2°. We observed a significant improvement of the photoluminescence intensity for the area with misorientation above 1.5°, which we attribute to the quenching of nonradiative recombination processes. From the structural point of view, the increase of the misorientation angle above 1.5° is accompanied by the improvement of the morphology of the sample and quality of the quantum wells observed through atomic force microscopy and transmission electron microscopy. We show that the structural and emission qualities in high-InN- mole fraction layers can be improved just by increasing the misorientation angle of the substrate and that the improved qualities are preserved even for large misorientation angles.

Characterization of the N-polar GaN film grown on C-plane sapphire and misoriented C-plane sapphire substrates by MOCVD

Gallium nitride (GaN) thin film of the nitrogen polarity (N-polar) was grown on C-plane sapphire and misoriented C-plane sapphire substrates respectively by metal-organic chemical vapor deposition (MOCVD). The misorientation angle is off-axis from C-plane toward M-plane of the substrates, and the angle is 2° and 4° respectively. The nitrogen polarity was confirmed by examining the images of the scanning electron microscope before and after the wet etching in potassium hydroxide (KOH) solution. The morphology was studied by the optical microscope and atomic force microscope. The crystalline quality was characterized by the x-ray diffraction. The lateral coherence length, the tilt angle, the vertical coherence length, and the vertical lattice-strain were acquired using the pseudo-Voigt function to fit the x-ray diffraction curves and then calculating with four empirical formulae. The lateral coherence length increases with the misorientation angle, because higher step density and shorter distance between adjacent steps can lead to larger lateral coherence length. The tilt angle increases with the misorientation angle, which means that the misoriented substrate can degrade the identity of crystal orientation of the N-polar GaN film. The vertical lattice-strain decreases with the misorientation angle. The vertical coherence length does not change a lot as the misorientation angle increases and this value of all samples is close to the nominal thickness of the N-polar GaN layer. This study helps to understand the influence of the misorientation angle of misoriented C-plane sapphire on the morphology, the crystalline quality, and the microstructure of N-polar GaN films.

Two-inch high-quality (001) diamond heteroepitaxial growth on sapphire (112̄0) misoriented substrate by step-flow mode

Two-inch-diameter high-quality free-standing (001) diamond layers were grown on misoriented (110) sapphire. The substrate misorientation allows step-flow growth, and tensile stress is released in the diamond layer. Consequently, the diamond layer delaminates naturally from the substrate without cracking. For the diamond grown on the sapphire misoriented by 7° toward the [100] direction, the widths of the (004) and (311) X-ray rocking curves were 98.35 and 175.3 arcsec, respectively, the lowest ever reported. The curvature radius of the diamond was 99.64 cm in the [100] direction and 260.21 cm in the [0001] direction of the substrate, the highest ever reported.

Effect of Substrate Misorientation on the Structural and Optical Characteristics of In-Rich InGaAs/GaAsP Quantum Wells

InGaAs quantum well (QW) lasers have attracted significant attention owing to their considerable potential for applications in optical communications; however, the relationship between the misorientation of the substrates used to grow InGaAs QWs and the structural and optical properties of QWs is still ambiguous. In this study, In-rich InGaAs/GaAsP single QWs were grown in the same run via metal organic chemical vapor deposition on GaAs (001) substrates misoriented by 0°, 2°, and 15° toward (111). The effects of substrate misorientation on the crystal quality and structural properties of InGaAs/GaAsP were investigated by X-ray diffraction and Raman spectroscopy. The 0° substrate exhibited the least lattice relaxation, and with increasing misorientation, the degree of lattice relaxation increased. The optical properties of the InGaAs/GaAsP QWs were investigated using temperature-dependent photoluminescence. An abnormal S-shaped variation of the peak energy and inverse evolution of the spectral bandwidth were observed at low temperatures for the 2° substrate, caused by the localization potentials due to the In-rich clusters. Surface morphology observations revealed that the growth mode varied with different miscuts. Based on the experimental results obtained in this study, a mechanism elucidating the effect of substrate miscuts on the structural and optical properties of QWs was proposed and verified.

Room-temperature spin–orbit magnetic fields in slightly misoriented (110) InGaAs/InAlAs multiple quantum wells

Spin–orbit (SO) magnetic fields caused by the Dresselhaus SO interaction in slightly misoriented (110) InGaAs/InAlAs quantum wells (QWs) are investigated using the time-resolved and spatially resolved optical Kerr rotation technique. The Dresselhaus SO magnetic field is directed along the in-plane in the (001) QWs and along the out-of-plane in the (110) QWs. On the contrary, in QWs grown on a slightly misoriented (110) substrate, the out-of-plane and in-plane components of the Dresselhaus SO magnetic field coexist. In this study, the strong out-of-plane and the in-plane SO magnetic fields peculiar to the misoriented (110) InGaAs QWs are revealed at room temperature by analyzing spatially resolved diffusion-driven spin precession dynamics with a diagonally applied external magnetic field. Based on the scan position dependence of the spin precession frequency induced by the SO magnetic field, the simultaneous observations of the out-of-plane and the in-plane SO magnetic fields are achieved and Dresselhaus SO parameter is extracted to be 1.9×10−12 eV m. This value accounts for the scan position dependencies with various magnetic fields and reveals the reliability of the extracted SO parameter.

Direct demonstration of carrier distribution and recombination within step-bunched UV-LEDs

AlGaN-based solid state UV emitters have many advantages over conventional UV sources. However, UV-LEDs still suffer from numerous challenges, including low quantum efficiency compared to their blue LED counterparts. One of the inherent reasons is a lack of carrier localization effect inside fully miscible AlGaN alloys. In the pursuit of phase separation and carrier localization inside the active region of AlGaN UV-LED, utilization of highly misoriented substrates proves to be useful, yet the carrier distribution and recombination mechanism in such structures has seldom been reported. In this paper, a UV-LED with step-bunched surface morphology was designed and fabricated, and the internal mechanism of high internal quantum efficiency was studied in detail. The correlation between microscale current distribution and surface morphology was provided, directly demonstrating that current prefers to flow through the step edges of the epitaxial layers. Experimental results were further supported by numerical simulation. It was found that efficient radiative recombination centers were formed in the inclined quantum well regions. A schematic three-dimensional energy band structure of the multiple quantum wells (MQWs) across the step was proposed and helps in further understanding the luminescence behavior of LEDs grown on misoriented substrates. Finally, a general principle to achieve carrier localization was proposed, which is valid for most ternary III-V semiconductors exhibiting phase separation.

Influence of GaAs substrate misorientation on gallium and arsenic evaporation rates

The dependence of the Ga and As evaporation rates on GaAs(111)A substrate misorientation was analyzed using Monte Carlo simulation. The gallium and arsenic desorption rates are proportional to the step density of vicinal substrates at congruent (layer-by-layer) evaporation. With incongruent evaporation (gallium droplet formation on the surface), the arsenic desorption rate weakly depends on the substrate misorientation and the gallium desorption rate is independent of it.

Influence of substrate misorientation on the emission and waveguiding properties of a blue (In,Al,Ga)N laser-like structure studied by synchrotron radiation microbeam X-ray diffraction

In this work, we study how an epitaxial laser-like (or superluminescent diode-like) structure is modified by intentional changes of the substrate misorientation in the range of 0.5°–2.6°. The 40 μm × 40 μm test structure with misorientation profiling was fabricated using multilevel photolithography and dry-etching. The local structural parameters were measured by synchrotron radiation microbeam X-ray diffraction, with the sampling area of below 1 μm × 1 μm . We directly obtained the relation between the misorientation and indium content in the quantum well, changing from 9% to 18%, with a high resolution (small misorientation step). We also show a good agreement of local photoluminescence emission wavelength with simulation of transition energy based on synchrotron radiation microbeam X-ray diffraction (SR-XRD) data and estimated Stokes shift. We observe that the substrate misorientation influences also the InGaN waveguide and AlGaN cladding composition. Still, we showed through simulation of the optical confinement factor of a full laser diode structure that good light guiding properties should be preserved in the whole misorientation range studied here. This proves the usefulness of misorientation modification in applications like broadband superluminescent diodes or multicolor laser arrays.

THz Radiation Measurement with HTSC Josephson Junction Detector Matched to Planar Antenna

Superconducting Josephson junctions have major advantages as detectors of millimeter wave radiation. Frequency of the radiation can be easily derived from the Shapiro steps of the current-voltage characteristics. However, system performance is highly sensitive to impedance mismatch between the antenna and the junction; therefore, optimization is essential. We analyzed and implemented an improved antenna structure, in which the junction is displaced from the antenna center and placed between the ends of two matching strips. Based on theoretical analysis and advanced electromagnetic simulations, we optimized strip dimensions, which affect both the detection magnitude and the frequency of the reflection coefficient dip. Accordingly, two Au bow-tie antennas with different matching strip widths were fabricated. Superconducting Yttrium Barium Copper Oxide (YBCO) thin films were deposited exactly at the bicrystal substrate misorientation points, forming Josephson junctions at the ends of two matching strips. We found a very high correlation between the simulations and the response to Radio Frequency (RF) radiation in the range of 145–165 GHz. Experimental results agree extremely well with the design, showing best performance of both antennas around the frequency for which impedance matching was derived.

Influence of substrate misorientation on the optical properties of Mg-doped GaN

The GaN substrate miscut angle has a significant effect on the optical properties of Mg-doped GaN grown by metal-organic chemical vapor deposition. We have studied the optical properties of epilayers grown on c-plane GaN wafers with nominal miscut angles of 0.3° and 4° toward the [11¯00] direction. Periodic surface steps are observed in thin films grown on 0.3° miscut substrates. The step separation and height, as well as the surface roughness, increase with layer thickness, leading to a decrease in Mg doping efficiency. For films grown on 4° miscut substrates, step bunching causes the formation of visually observable wavy features on the film surface with strong spatial variations in cathodoluminescence characteristics, indicating a significant effect of surface morphology on the nature of Mg incorporation and p-type characteristics.

Unambiguously Enhanced Ultraviolet Luminescence of AlGaN Wavy Quantum Well Structures Grown on Large Misoriented Sapphire Substrate

AbstractHigh‐quality epitaxy consisting of Al1−xGaxN/Al1−yGayN multiple quantum wells (MQWs) with sharp interfaces and emitting at ≈280 nm is successfully grown on sapphire with a misorientation angle as large as 4°. Wavy MQWs are observed due to step bunching formed at the step edges. A thicker QW width accompanied by a greater accumulation of gallium near the macrostep edge than that on the flat‐terrace is observed on 4° misoriented sapphire, leading to the generation of potential minima with respect to their neighboring QWs. Consequently, a significantly enhanced photoluminescence intensity (at least ten times higher), improved internal quantum efficiency (six times higher at low excitation laser power), and a much longer carrier lifetime are achieved. Importantly, the wafer‐level output‐power of the ultraviolet light emitting diodes on 4° misoriented substrate is nearly increased by 2–3 times. This gain is attributed to the introduction of compositional inhomogeneities in AlGaN alloys induced by gallium accumulation at the step‐bunched region thus forming a lateral potential well for carrier localization. The experimental results are further confirmed by a numerical modeling in which a 3D carrier confinement mechanism is proposed. Herein, the compositional modulation in active region arising from the substrate misorientation provides a promising approach in the pursuit of high‐efficient ultraviolet emitters.

Nanoscale contact behavior of (1 1 1) fcc metallic surfaces

With the use of molecular dynamics simulations, the contact between two substrates made of the same material is investigated for three different fcc metals: Al, Cu, and Ag. For this purpose, two misoriented substrates containing (1 1 1) planes parallel to their surfaces are placed at varied interfacial separations and allowed to form a contact. While JC happens in all three materials, it is shown that, as opposed to Al and Ag, Cu exhibits a smooth jump-to-contact (JC) behavior, meaning that for separations just above the critical distance for JC, the two surfaces get closer to each other, but they do not form a contact. On the other hand, for separations below the critical distance, JC occurs, and dislocations are generated at the interface due to the misorientation between substrates. It is seen that under favorable conditions, the interfacial dislocations can multiply, primarily because of the strain that exists in the system due to the initial interfacial separation. The possibility of occurrence of dislocation multiplication is found to be higher at high contact temperatures, high strain values, and low misorientation angles. Also, Al is found to be less prone to dislocation multiplication, compared to Ag and Cu. Most importantly, it is observed that the predominant mechanism for dislocation multiplication in Al is cross-slip of interfacial dislocations, whereas in Ag and Cu it is the nucleation of partial dislocations from the interface.

Influence of substrate misorientation on carbon impurity incorporation and electrical properties of p-GaN grown by metalorganic chemical vapor deposition

The influence of substrate misorientation angle on carbon impurity incorporation and electrical properties of p-GaN grown at a low temperature of 900 °C has been explored. Secondary ion mass spectrometry results reveal that the concentration of unintentionally incorporated carbon impurity decreases remarkably (from 2 × 1017 cm−3 to 7 × 1016 cm−3) with the increasing misorientation angle. The step motion model is introduced to explain the reason for decreasing carbon concentration with increasing misorientation angle. It has also been found the hole concentration of p-GaN increases and the resistivity of p-GaN decreases with the increasing misorientation angle since carbon acts as compensating donor in p-GaN.

Influence of GaAs substrate misorientation on the characteristics in undulating compositional step-graded AlGaInAs buffers

Undulating compositional step-graded AlGaInAs buffers are applied to transit the lattice mismatch of 3.8% between InP cap layer and GaAs substrates with misorientation of 2°, 7° and 15° toward (111)A by metal organic chemical vapor deposition (MOCVD). The surface morphology and strain relaxation are strongly dependent on the substrate misorientation. The sample grown on 15° GaAs substrate showed a substantial improvement of surface roughness and reduction of dislocation pile-up densities compared with that on the 2° and 7° substrate. The experiment results showed that the substrate with 15° misorientation can maintain a smooth epitaxial film surface by increasing the possibility of atoms incorporating into the lattice and ease the imbalance of the misfit strain stress distributed between different slip systems to make dislocations distributed more uniformly, which can reduce the strain field to exaggerate the channel width for dislocation gliding along the interface and decrease the threading dislocation densities. Overall, this work provides a promising way to obtain virtual substrates for the achievement of desired metamorphic devices.