The Blue Laser Diode

With the increasing requirements for microelectromechanical systems (MEMS) regarding stability, miniaturization and integration, novel materials such as wide band gap semiconductors are attracting more attention. Polycrystalline SiC has first been implemented into Si micromachining techniques, mainly as etch stop and protective layers. However, the outstanding properties of wide band gap semiconductors offer many more possibilities for the implementation of new functionalities. Now, a variety of technologies for SiC and group III nitrides exist to fabricate fully wide band gap semiconductor based MEMS. In this paper we first review the basic technology (deposition and etching) for group III nitrides and SiC with a special focus on the fabrication of three-dimensional microstructures relevant for MEMS. The basic operation principle for MEMS with wide band gap semiconductors is described. Finally, the first applications of SiC based MEMS are demonstrated, and innovative MEMS and NEMS devices are reviewed.

http://iopscience.iop.org/article/10.1088/0022-3727/40/20/S19/pdf

Group III nitride and SiC based MEMS and NEMS: materials properties, technology and applications

Introduction Properties of Semiconductors Introduction Crystallographic Properties Lattice Constants and Thermal Expansion Coefficients Elastic Properties Surface Free Energy Dislocations Planar Defects Problems References Heteroepitaxial Growth Introduction Vapor Phase Epitaxy (VPE) Molecular Beam Epitaxy (MBE) Silicon, Germanium, and Si1-xGex Alloys Silicon Carbide III-Arsenides, III-Phosphides, and III-Antimonides III-Nitrides II-VI Semiconductors Conclusion Problems References Surface and Chemical Considerations in Heteroepitaxy Introduction Surface Reconstructions Nucleation Growth Modes Nucleation Layers Surfactants in Heteroepitaxy Quantum Dots and Self-Assembly Problems References Mismatched Heteroepitaxial Growth and Strain Relaxation Introduction Pseudomorphic Growth and the Critical Layer Thickness Dislocation Sources Interactions between Misfit Dislocations Lattice Relaxation Mechanisms Quantitative Models for Lattice Relaxation Lattice Relaxation on Vicinal Substrates: Crystallographic Tilting of Heteroepitaxial Layers Lattice Relaxation in Graded Layers Lattice Relaxation in Superlattices and Multilayer Structures Dislocation Coalescence, Annihilation, and Removal in Relaxed Heteroepitaxial Layers Thermal Strain Cracking in Thick Films Problems References Characterization of Heteroepitaxial Layers Introduction X-Ray Diffraction Electron Diffraction Microscopy Crystallographic Etching Techniques Photoluminescence Growth Rate and Layer Thickness Composition and Strain Determination of Critical Layer Thickness Crystal Orientation Defect Types and Densities Multilayered Structures and Superlattices Growth Mode Problems References Defect Engineering in Heteroepitaxial Layers Introduction Buffer Layer Approaches Reduced Area Growth Using Patterned Substrates Patterning and Annealing Epitaxial Lateral Overgrowth (ELO) Pendeo-Epitaxy Nanoheteroepitaxy Planar Compliant Substrates Free-Standing Semiconductor Films Conclusion Problems References Appendix A: Bandgap Engineering Diagrams Appendix B: Lattice Constants and Coefficients of Thermal Expansion Appendix C: Elastic Constants Appendix D: Critical Layer Thickness Appendix E: Crystallographic Etches Appendix F: Tables for X-Ray Diffraction Index

Heteroepitaxy of Semiconductors: Theory, Growth, and Characterization

Stress-Induced Self-Organization of Nanoscale Structures in SiGe/Si Multilayer Films

This paper reviews the progress of N-polar () GaN high frequency electronics that aims at addressing the device scaling challenges faced by GaN high electron mobility transistors (HEMTs) for radio-frequency and mixed-signal applications. Device quality (Al, In, Ga)N materials for N-polar heterostructures are developed using molecular beam epitaxy and metalorganic chemical vapor deposition. The principles of polarization engineering for designing N-polar HEMT structures will be outlined. The performance, scaling behavior and challenges of microwave power devices as well as highly-scaled depletion- and enhancement-mode devices employing advanced technologies including self-aligned processes, n+ (In,Ga)N ohmic contact regrowth and high aspect ratio T-gates will be discussed. Recent research results on integrating N-polar GaN with Si for prospective novel applications will also be summarized.

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N-polar GaN epitaxy and high electron mobility transistors

We have studied the surface kinetics of N-face GaN during molecular-beam epitaxial growth by investigating the Ga wetting and the surface morphology. In the case of N-face GaN, it is not possible to establish the self-regulated Ga bilayer that is used as a surfactant for molecular-beam-epitaxy growth of Ga-face GaN. Indeed, to prevent the accumulation of Ga droplets, growth of the N-face GaN must be performed with less than one monolayer of excess Ga on the growing surface. Optimum surface morphology is achieved when growth is performed at the Ga accumulation limit.

Growth kinetics of N-face polarity GaN by plasma-assisted molecular-beam epitaxy

We report on the effect of vertical correlation on GaN/AlN quantum dots grown by plasma-assisted molecular-beam epitaxy using the modified Stranski–Krastanow growth mode. When increasing the number of GaN periods, we observe a homogenization of the island distribution and a redshift of the luminescence line. This redshift is attributed to an increase of the quantum Stark effect due to the increase of the piezoelectric contribution to the internal electric field.

Effects of stacking on the structural and optical properties of self-organized GaN/AlN quantum dots

The growth mode of N-face GaN deposited on AlN(0001¯) by plasma-assisted molecular beam epitaxy has been investigated. Based on reflection high-energy electron diffraction experiments, we demonstrate that for appropriate Ga fluxes and substrate temperature, a self-regulated 1‐ML-thick Ga excess film can be formed on the growing surface. Depending on the presence of this Ga monolayer, the growth can proceed following either the Stranski–Krastanow or the Frank Van der Merwe growth modes, hence enabling the synthesis of either quantum dots or quantum wells.

Surfactant effect of gallium during the growth of GaN on AlN(0001¯) by plasma-assisted molecular beam epitaxy

Due to the large difference in lattice parameters and thermal expansion coefficients, the hetero-epitaxial growth of 3C-SiC on Si mainly results in highly defective layers on strongly bent wafers. The defects may not be detrimental for very basic applications, but the bow is. In order to solve this problem, we have developed a technique called checker-board carbonization which, basically, balances a compressive (interfacial) stress by a tensile one. In this way, the overall bending is effectively reduced. In this work, we will report on the effect of polishing the thick, as-grown, 3C-SiC layers deposited on top and results from, both, infrared and Raman spectroscopy collected on 35 mm diameter wafers will be presented. From DDX and low temperature photoluminescence measurements, we will show that a similar 3C-SiC quality can be achieved on, both, parts of the initially compressive and tensile re-grown layers.

Control of 3C-SiC/Si wafer bending by the "checker-board" carbonization method

We have investigated the polytype conversion of a GaN film from N-face wurtzite (2H) to zinc-blende (3C) structure due to Mg doping during growth by plasma-assisted molecular-beam epitaxy. Structural analysis by high-resolution transmission electron microscopy and high-resolution x-ray diffraction measurement revealed alignment of the cubic phase with the [111] axis perpendicular to the substrate surface. The optical characteristics of GaN:Mg layers are shown to be very sensitive to the presence of the cubic polytype. For low Mg doping, photoluminescence is dominated by a phonon-replicated donor-acceptor pair at ∼3.25eV, related to the shallow Mg acceptor level, accompanied by a narrow excitonic emission. For high Mg doping, the photoluminescence spectra are also dominated by a line around 3.25eV, but this emission displays the behavior of excitonic luminescence from cubic GaN. A cubic-related donor-acceptor transition at ∼3.16eV is also observed, together with a broad blue band around 2.9eV, previously...

Hugues Mank

Papers

Growth kinetics of N-face polarity GaN by plasma-assisted molecular-beam epitaxy

Effects of stacking on the structural and optical properties of self-organized GaN/AlN quantum dots

Surfactant effect of gallium during the growth of GaN on AlN(0001¯) by plasma-assisted molecular beam epitaxy

Control of 3C-SiC/Si wafer bending by the "checker-board" carbonization method

Polytype transition of N-face GaN:Mg from wurtzite to zinc-blende