Search

The effect of the inversion of polarity in gallium nitride layers from the N-polar GaN layer to the Ga-polar GaN layer was discovered during the sequential growth of GaN films on hybrid SiC/Si(111) substrates by nitrogen plasma-assisted molecular beam epitaxy and chloride–hydride vapor phase epitaxy. A new method has been developed for the formation of crack-free Ga-polar GaN/AlN heterostructures on hybrid SiC/Si(111) substrates. The method includes two stages of growing gallium nitride layers. At the first stage, the transient N-polar GaN layer is grown on the SiC/Si(111) surface by nitrogen plasma-assisted molecular beam epitaxy. At the second stage, two layers are grown on the obtained N-polar GaN layer by chloride–hydride vapor phase epitaxy, namely, the AlN layer and then the GaN layer, which at this stage grows in the Ga-polar orientation. Etching in a KOH solution affects only the N-polar GaN transition layer and leads to its complete removal. This procedure separates the main Ga-polar GaN layer from the SiC/Si(111) substrate completely. The method enables one to grow crack-free and elastically unstressed thick GaN layers and transfer them to substrates of other materials.

Two different approaches for the etching of the gallium nitride epitaxial layers grown on Si(111) substrates by plasma-assisted molecular beam epitaxy have been elaborated. It is demonstrated that anisotropic etch profiles can be achieved by both photoenhanced wet chemical etching and reactive plasma-chemical etching methods. Moreover, it is shown, that the photoenhanced wet chemical etching allows to remove GaN layer without damaging silicon substrate.

The AlN/Si(111) epitaxial structures were synthesized by coalescence overgrowth of AlN nanocolumns using PA MBE technique. Such epitaxial structures can be used as a buffer layer for obtaining high quality AlN and GaN layers. Structural, electrical and chemical properties of these samples were studied. For the first time it was demonstrated that the etching of the obtained type of AlN/Si(111) structures in KOH can become a promising method for obtaining high quality free-standing AlN and GaN.

A new method for nanopit formation by molecular-beam epitaxy (MBE) on different silicon substrates has been investigated. The dependence of the shape and depth of the nanopits on substrate orientation and doping type has been studied. The samples with an array of nanopits with 25 nm depth and (2-6)·108 cm−2 density for subsequent monolithic selective growth of quantum dots (QD) have been created.

The dependence of the crystallographic polarity of GaN epitaxial layers produced by nitrogen plasma-enhanced molecular-beam epitaxy on Si(111) substrates on the nitridation parameters and initial growth conditions has been studied. A rapid procedure for determining the polarity of GaN epitaxial layers was developed. It was found experimentally that the nitridation parameters of the silicon substrate have no effect on the polarity of a GaN layer. It was shown that the substrate temperature in the stage of nucleation of a GaN epitaxial layer is one of the factors determining its polarity.

An approach to precision calibration of the silicon doping level in gallium arsenide epitaxial layers is discussed that is based on studying the dependence of the carrier density in the test GaAs layer on the silicon- source temperature using the Hall-effect and CV profiling techniques. The parameters are measured by standard or certified measuring techniques and approved measuring instruments. It is demonstrated that the use of CV profiling for controlling the carrier density in the test GaAs layer at the thorough optimization of the measuring procedure ensures the highest accuracy and reliability of doping level calibration in the epitaxial layers with a relative error of no larger than 2.5%.

The n+-GaN epilayers were synthesised by PA MBE on the SiO2 patterned GaN/c-Al2O3 templates, grown by MOCVD. Formation of the polycrystalline GaN atop of the SiO2 mask during PA MBE was observed. It was found that macroscopic voids at the interface polycrystalline GaN/SiO2/n-GaN template appeared during the PA MBE process. The polycrystalline GaN film was completely removed by etching in hot aqueous KOH solution. Hall measurements have shown that the value of electron concentration in n+-GaN contact layer is about ne∼4.6×1019 cm-3.

The combination of high operation temperatures and small diode lasers directly grown on silicon substrates is essential for their application in future photonic integrated circuits. In this letter, results are presented for quantum dot III–V-on-Si microdisk diode lasers tested at elevated temperatures. To the best of our knowledge, we have demonstrated the first uncooled microlasers with diameter of 30 µm capable of operating in the continuous wave regime at 60 °C. In the lasing regime, the emission spectra contain one very intense line with a full-width at half-maximum of 30 pm; the side mode suppression ratio reaches 18 dB. Because of self-heating, the actual temperature of the active region is close to 100 °C. Under pulsed excitation, the maximal lasing temperature is 110 °C.

In this work the effects of H3PO4:CH3COOH:HNO3:HF etching solution taken with different concentrations to the Ga-polar GaN/SixNy/Si(111) epitaxial structures is investigated. Possibility of at least partial separation of Ga-polar GaN film from the silicon substrate without any GaN surface morphology changes by the selected etchants is demonstrated. The etching process mechanism is shown. Resistivity of the photoresist mask to etchants used in the experiments is found.