Gallium nitride (GaN) and its allied binaries InN and AIN as well as their ternary compounds have gained an unprecedented attention due to their wide-ranging applications encompassing green, blue, violet, and ultraviolet (UV) emitters and detectors (in photon ranges inaccessible by other semiconductors) and high-power amplifiers. However, even the best of the three binaries, GaN, contains many structural and point defects caused to a large extent by lattice and stacking mismatch with substrates. These defects notably affect the electrical and optical properties of the host material and can seriously degrade the performance and reliability of devices made based on these nitride semiconductors. Even though GaN broke the long-standing paradigm that high density of dislocations precludes acceptable device performance, point defects have taken the center stage as they exacerbate efforts to increase the efficiency of emitters, increase laser operation lifetime, and lead to anomalies in electronic devices. The p...

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Luminescence properties of defects in GaN

Kelvin probe force microscopy and its application

The recent development in the field of superhard materials with Vickers hardness of ⩾40 GPa is reviewed. Two basic approaches are outlined including the intrinsic superhard materials, such as diamond, cubic boron nitride, C3N4, carbonitrides, etc. and extrinsic, nanostructured materials for which superhardness is achieved by an appropriate design of their microstructure. The theoretically predicted high hardness of C3N4 has not been experimentally documented so far. Ceramics made of cubic boron nitride prepared at high pressure and temperature find many applications whereas thin films prepared by activated deposition from the gas phase are still in the stage of fundamental development. The greatest progress has been achieved in the field of nanostructured materials including superlattices and nanocomposites where superhardness of ⩾50 GPa was reported for several systems. More recently, nc-TiN/SiNx nanocomposites with hardness of 105 GPa were prepared, reaching the hardness of diamond. The principles of de...

https://mediatum.ub.tum.de/doc/958917/file.pdf

The search for novel, superhard materials

Characterization of amorphous and nanocrystalline carbon films

Ionic conduction in space charge regions

Important structural characteristics (correlation lengths of columnar crystallites, dislocation densities, angles of rotational disorder) of hexagonal GaN grown by metallorganic chemical vapour deposition on c-plane sapphire are determined by transmission electron microscopy and triple-axis X-ray diffractometry. GaN films exhibit an edge dislocation density in the range of 1011 cm−2, a tilt and twist angle of 0.1° and 1.3° and a columnar structure with a lateral and vertical correlation length of 150 and 1000 nm respectively. The determination of correlation lengths and dislocation densites from X-ray patterns was undertaken using two independent evaluation methods which are discussed in detail. It is also shown that triple-axis X-ray diffractometry is a highly suitable technique for the separation of different kinds of structural defects such as edge and screw dislocations that lead to a characteristic broadening of symmetric and asymmetric Bragg reflections. The correlation lengths and dislocat...

Defect structure of epitaxial GaN films determined by transmission electron microscopy and triple-axis X-ray diffractometry

Experimental studies on aluminum (Al) and boron (B) implantation in 4H/6H SiC are reported; the implantation is conducted at room temperature or elevated temperatures (500 to 700 C). Both Al and B act as ``shallow`` acceptors in SiC. The ionization energy of these acceptors, the hole mobility and the compensation in the implanted layers are obtained from Hall effect investigations. The degree of electrical activity of implanted Al/B atoms is determined as a function of the annealing temperature. Energetically deep centers introduced by the Al{sup +}/B{sup +} implantation are investigated. The redistribution of implanted Al/B atoms subsequent to anneals and extended lattice defects are monitored. The generation of the B-related D-center is studied by coimplantation of Si/B and C/B, respectively. (orig.) 60 refs.

Doping of SiC by Implantation of Boron and Aluminum

Polycrystalline Semiconductors II

In this letter we present calculations by three‐dimensional finite element method and measurements by convergent beam electron diffraction of the displacement field resulting from misfitting Ge0.85Si0.25 islands on Si(001). A good agreement between the results of both methods indicates that the three‐dimensional finite element method is a reliable tool to calculate the strain, and thus the stress field, in such nanostructures. As a result both methods show that the substrate substantially takes part in the elastic relaxation process in such heteroepitaxial systems.

Strained state of Ge(Si) islands on Si: Finite element calculations and comparison to convergent beam electron‐diffraction measurements

We study the interplay of elastic and plastic strain relaxation of SiGe/Si(001). We show that the formation of crosshatch patterns is the result of a strain relaxation process that essentially consists of four subsequent stages: (i) elastic strain relaxation by surface ripple formation; (ii) nucleation of dislocations at the rim of the substrate followed by dislocation glide and deposition of a misfit dislocation at the interface; (iii) a locally enhanced growth rate at the strain relaxed surface above the misfit dislocations that results in ridge formation. These ridges then form a crosshatch pattern that relax strain elastically. (iv) Preferred nucleation and multiplication of dislocations in the troughs of the crosshatch pattern due to strain concentration. The preferred formation of dislocations again results in locally enhanced growth rates in the trough and thus leads to smoothing of the growth surface.

Horst P. Strunk

Papers

Defect structure of epitaxial GaN films determined by transmission electron microscopy and triple-axis X-ray diffractometry

Doping of SiC by Implantation of Boron and Aluminum

Polycrystalline Semiconductors II

Strained state of Ge(Si) islands on Si: Finite element calculations and comparison to convergent beam electron‐diffraction measurements

Surface ripples, crosshatch pattern, and dislocation formation: Cooperating mechanisms in lattice mismatch relaxation