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In the first part of this paper, we present a model that explains and determines quantitatively the twists between nucleation islands in the case of a Volmer–Weber heteroepitaxial growth of tetrahedrally coordinated semiconductors along hexagonal orientations. These twists are caused by the network of the screw components of the 60° misfit dislocations. The orientations of the screw components are distributed randomly, and the maximum twist is obtained when all the screw components have the same orientation. The maximum twists are related to the density of misfit dislocations and, therefore, increase with the mismatch between the deposited materials and their substrate. In the second part of the paper, we study five systems having a large distribution of mismatches from 4% to 19%. For the four systems fulfilling the conditions necessary for the application of the model (plastic relaxation of grown islands), the measured maximum twists fit with the calculated values, thereby validating the model. The twists of nucleation islands are related to the mismatch and are, therefore, intrinsic to the material systems. The defects created at the coalescence of twisted islands determine the initial microstructure/defect distribution of the nucleation layer. [ABSTRACT FROM AUTHOR]

Off-axis electron holography has been used to measure the width of the depletion region in a series of tunnel junction GaN light emitting diodes that have been prepared using different growth processes for blue emission. The total measured potentials are combinations of the mean inner potential, dopant potential, and piezoelectric contributions. The dopant potential has been unmixed from the mean inner potential such that the width of the tunnel junctions in the different diodes can be measured. The experimental results are then compared to secondary ion mass spectrometry, simulations, and opto-electronic testing. We find that the measured tunnel junction widths are consistent with simulations as well as the current density and voltage characteristics. As such, off-axis electron holography has been demonstrated as a unique technique that can be used to reproducibly measure the electrostatic potentials in tunnel junctions with nm-scale resolution in real III–V device specimens. [ABSTRACT FROM AUTHOR]

The use of tunnel junctions (TJs) is a potential solution in blue light-emitting diodes (LEDs) to poor p-contacts, replacing it with another n-contact. TJs are even more advantageous for UV-emitting structures, which suffer from considerably low injection efficiency in high Al concentration UV LEDs. In this article, we report our work on Ge n-doped GaN and AlGaN TJs grown on top of blue and UV LEDs, respectively, by a hybrid growth method. We have achieved state-of-the-art mobility (67 cm2/V s) and resistivity (1.7 × 10−4 Ω cm) at a free electron concentration of 5.5 × 1020 cm−3 in Ge-doped GaN. With an emission wavelength of 436 nm, the GaN TJ slightly increased the optical power of the blue LED. The AlGaN TJs, on the other hand, improved the optical power of the UV LED (304 nm) by at least a factor of 3, suggesting the enhancement of the hole injection efficiency by the use of TJs in UV-emitting structures. [ABSTRACT FROM AUTHOR]

We demonstrate the growth of almost strain-free (10-11) semipolar GaN on silicon-on-insulator (SOI) substrates, with no meltback etching and with a defect density strongly reduced compared to semipolar templates grown on patterned silicon substrates. This is carried out using SOI substrates with a very thin (∼150 nm) 6° off (001) Si top layer. By resorting to very small nucleation (111) facets, revealed through chemical etching of the topmost thin Si layer, we are able to diminish significantly the overall dislocation density. Cathodoluminescence and scanning electron microscopy images at different stages of the growth illustrate how the defect density reduction operates and confirm the complete suppression of meltback etching over the whole 2 in. wafer. Low temperature photoluminescence and optical reflectivity indicate that complete strain relaxation is closely achieved (D0X at 3.473 ± 0.001 eV), compared to semipolar epilayers grown onto "bulk" silicon (D0X at 3.460 eV). Thanks to this efficient strain relaxation, very thick layers, up to 9 μm, could be obtained crack-free. [ABSTRACT FROM AUTHOR]

AlN-on-Si can be considered as a model system for heteroepitaxial growth of highly mismatched materials. Indeed, AlN and Si drastically differ in terms of chemistry, crystalline structure, and lattice parameters. In this paper, we present a transmission electron microscopy and grazing incidence X-ray diffraction study of the microstructure of AlN layers epitaxially grown on Si (111) by molecular beam epitaxy. The large interfacial energy due to the dissimilarities between AlN and Si results in a 3D Volmer-Weber growth mode with the nucleation of independent and relaxed AlN islands. Despite a well-defined epitaxial relationship, these islands exhibit in-plane misorientations up to 6°–7°. We propose a model which quantitatively explains these misorientations by taking into account the relaxation of the islands through the introduction of 60° a-type misfit dislocations. Threading dislocations (TDs) are formed to compensate these misorientations when islands coalesce. TD density depends on two parameters: the islands' misorientation and density. We show that the former is related to the mismatch between AlN and Si, while the latter depends on the growth parameters. A large decrease in TD density occurs during the 3D growth stage by overlap and overgrowth of highly misoriented islands. On the other hand, the TD density does not change significantly when the growth becomes 2D. The proposed model, explaining the misorientations of 3D-grown islands, may be extended to other (0001)-oriented III-nitrides and more generally to any heteroepitaxial system exhibiting a 3D Volmer-Weber growth mode with islands relaxed thanks to the introduction of mixed-type misfit dislocations. [ABSTRACT FROM AUTHOR]

The effects of chlorine doping of thick polycrystalline CdTe layers grown by close space sublimation on their crystalline structure and the compensation and passivation processes are investigated. While the radiative emission of small grains is mainly attributed to compensating complexes implying chlorine and Cd vacancies, in larger grains, the luminescence comes from deeper levels most probably associated with compensating complexes implying residual impurities.

Research was conducted to examine in situ the kinetics changes in the growth of GaN induced by the presence of In segregated on the surface the the use of reflection high energy electron diffraction intensity oscillations. Findings demonstrate that In affected both Ga and N surface kinetics which resulted in the growth rate associated with a change in the amount of Ga and N effectively available for the GaN growth.

Micro-Raman spectroscopy, photoluminescence, x-ray diffraction and reflection high-energy electron diffraction are used to examine molecular beam epitaxy of cubic gallium nitrate on silicon carbide films deposited by chemical vapor deposition on silicon. Results showed that the wurtzite/zinc-blende ratio is influenced by N/metal ratio and the initial substrate roughness.

Research was conducted to examine the growth kinetics and optical properties of self-organized GaN quantum dots. They were fabricated by controlling the Stranski-Krastanov growth mode of GaN deposited by molecular beam epitaxy on AlN. Observations include evidence for the ripening of dots under vacuum which results in changes in dot size distribution. Results also indicate the strongly zero-dimensional character of the nanostructures.

Atomic layer epitaxy (ALE) was studied for the binary semiconductor MgTe. Reflection high-energy electron-diffraction studies on MgTe atomic deposition, together with x-ray diffraction, high-resolution transmission electron microscopy, and photoluminescence experiments on ALE-grown CdTe/MgTe superlattices were conducted. Findings showed that an autoregulated growth at 0.7+/-0.1 MgTe monolayer/ALE cycle can be attained in a substrate temperature range between 260 and 300 degrees C.

The growth of CdMnTe epilayers is described with emphasis on the misfit strain relaxation and the effect of this strain on the quality and structure of the epilayers. The description is obtained by using transmission electron microscopy, cathodoluminescence imaging and X-ray diffraction methods. The description reveals the correlation between the structural and optical properties of the elastically relaxed layers.

High resolution electron microscopy (HREM) was used to study strain mapping of ultrathin epitaxial MnTe and ZnTe layers that were grown in CdTe. This method revealed the total Zn amount per period and Zn location within each portion of the heterostructure. HREM generated images of individual interfaces with atomic resolution.

In this work, we present the fabrication and the characterization of an optical waveguide made of AlN and GaN layers grown by MBE on a Si(111) substrate. For the fundamental mode at 633 nm, the propagation losses are in the order of 2 dB/cm, which is a good number for SC waveguides at this wavelength. The propagation losses dramatically increase with the mode order. A careful comparison of measurements and modeling of the complete structure allows identifying the part of the losses due to absorption in the Si substrate, and showing that propagation losses could be further reduced by using well chosen SOI substrates.

In this article, we report on ZnO nanowires that were phosphorus doped using a spin on dopant glass deposition and diffusion method. Photoluminescence measurements suggest that this process yields p-doped ZnO. The spatial location of P atoms was studied using x-ray near-edge absorption structure spectroscopy and it is concluded that the doping is amphoteric with P atoms located on both Zn and O sites. [ABSTRACT FROM AUTHOR]

HgCdTe films grown by liquid phase epitaxy with different Cd compositions were post-annealed to control the Hg vacancy concentration. Then temperature-dependent Hall measurements and photoluminescence measurements allowed us to study the evolution of the Hg vacancy acceptor levels with the cadmium composition. For Cd compositions below 33% the Hg vacancies in HgCdTe present a negative-U property with the ionized state V- stabilized compared to the neutral state V0. For Cd compositions higher than 45%, the Hg vacancies in HgCdTe present a more standard level ordering with the ionized state V- at higher energy than the neutral state V0. [ABSTRACT FROM AUTHOR]