Dimiter Alexandrov

Excitons of the structure in wurtzite InxGa1−xN and their properties

Abstract The observed spectral blue shift of the electroluminescence in quantum well structures on In x Ga 1− x N is explained on the basis of existence of newfound excitons connected with the electron band structure of this semiconductor. New method for calculation of the electron band structure of multinary compound alloys is developed in the paper. This method takes into consideration that the electron energy depends on both the electron wave vector and the structure of the multinary crystal. The LCAO electron band structure of wurtzite In x Ga 1− x N is determined by this method as function of both the electron wave vector and the electron radius vector. New type of exciton called exciton of the structure is found on the basis of the electron band structure of wurtzite In x Ga 1− x N. The binding energy and the hydrogen like energy levels of the excitons of the structure are found. It is found that the movement of the excitons of the structure is possible only by tunneling and that these excitons are localized. It is found that destroying of these excitons has place in their interactions with hetero-junction and the observed spectral blue shift is explained on the basis of electrons and holes of exciton origin generated in this destroying.

Energy band gaps of InN containing oxygen and of the InxAl1−xN interface layer formed during InN film growth

The effect of known growth artifacts on the absorption and photoluminescence properties of InN films is determined using linear combination of atomic orbitals electron band structure calculations. InxAl1−xN interfacial layers are examined for various atomic fractions of Al, since these layers are observed to be relatively thick (up to 100 nm) for thin films of InN deposited on AlN or sapphire. It is found that for penetration of Al atoms in InN, forming In-rich InxAl1−xN, a decrease of the energy band gap of InN occurs, despite AlN having a much larger band gap than InN. Γc13↔Γν154 exciton emissions for InxAl1−xN are found to have an energy of 0.765–0.778 eV and may explain recent photoluminescence data for InN. Optical absorption for this alloy is dominated by a 1.58–1.62 eV transition. The second artifact investigated here is high concentration oxygen impurity atoms in wurtzite InN. Segregated oxygen species are not considered, only alloyed species with oxygen substituting on the nitrogen site. For this arrangement a new ternary semiconductor InOyN1−y with y∼0.1 is identified. A model of the tetrahedral cell In–O is made and the energy band gap of InOyN1−y is calculated. It is found that the presence of O atoms in InN can decrease the energy band gap. Optical absorption as low as 1.19 eV can be evident. The exciton emissions Γc12↔Γν151 in InOyN1−y were found to vary in energy over the range 0.84–1.01 eV.The effect of known growth artifacts on the absorption and photoluminescence properties of InN films is determined using linear combination of atomic orbitals electron band structure calculations. InxAl1−xN interfacial layers are examined for various atomic fractions of Al, since these layers are observed to be relatively thick (up to 100 nm) for thin films of InN deposited on AlN or sapphire. It is found that for penetration of Al atoms in InN, forming In-rich InxAl1−xN, a decrease of the energy band gap of InN occurs, despite AlN having a much larger band gap than InN. Γc13↔Γν154 exciton emissions for InxAl1−xN are found to have an energy of 0.765–0.778 eV and may explain recent photoluminescence data for InN. Optical absorption for this alloy is dominated by a 1.58–1.62 eV transition. The second artifact investigated here is high concentration oxygen impurity atoms in wurtzite InN. Segregated oxygen species are not considered, only alloyed species with oxygen substituting on the nitrogen site. For this...

Gallium Nitride Film Growth Using a Plasma Based Migration Enhanced Afterglow Chemical Vapor Deposition System

Gallium nitride layers were grown by a new migration enhanced epitaxy technique called MEAglow. Initial experiments were performed to characterize the plasma source used and to examine the surfaces of thin samples grown by the technique. Atomic force microscopy (AFM) results show root mean square (RMS) surface roughness values of less than 1 nm for samples grown at 650 °C, this is commensurate with Ga-face material grown directly on nitrided sapphire substrates.

Dependence of the magnetic properties of MnGaN epitaxial layers on external electrical field

Investigation of the magnetic properties of MnGaN epitaxial layers as a function of external electrical field was performed on the basis of field effect structure. The structure included substrate of n-type GaN, epitaxial layer of n-type MnxGa1-xN, dielectric layer and metal layer acting as field effect device gate. Each Mn atom in MnxGa1-xN contributes 4 net spins due to the electrons occupying energy levels 4F, 4D, 4P and 4G belonging to 3d orbital, and these levels are in the energy band gap and in the top of the valence band of MnxGa1-xN. The position of the Fermi level is determined to be in the energy band gap of the layer of GaN and to be above the level 4F in the layer of MnxGa1-xN. In this way application of external negative voltage on the gate causes change in the number of electrons contributing net spins and the saturation magnetization Msat of MnxGa1-xN changes as well. It was found that Msat changes in the range 1.15 × 10−3–0.7 × 10−3 A μm−1 if the external voltage changes in the interval 0–−5V. The application of this structure for the design of spintronic devices is discussed in this paper.

Complementary field effect transistors for VLSI design on GaN and related alloys

Newfound quasi-particles in In/sub x/Ga/sub 1-x/N called excitons of the structure are used as the basis for the design of complementary n-channel and p-channel field effect transistors in this paper. These complementary transistors are applicable for VLSI design. The transistors use excitons of the structure as both quantum electron source for n-channel and quantum hole source for p-channel. Both FET channels are designed on non-doped GaN. The design of the electron source of the n-channel and the design of the hole source of the p-channel are given. The designs of both FET structures are given as well. The corresponding voltage-current characteristics presenting the dependences of the drain currents on the voltages drain-source and on the gate voltages are given. The switching times of both field effect transistors (n-channel and p-channel) are determined.

Engineering of III-Nitride Semiconductors on Low Temperature Co-fired Ceramics

This work presents results in the field of advanced substrate solutions in order to achieve high crystalline quality group-III nitrides based heterostructures for high frequency and power devices or for sensor applications. With that objective, Low Temperature Co-fired Ceramics has been used, as a non-crystalline substrate. Structures like these have never been developed before, and for economic reasons will represent a groundbreaking material in these fields of Electronic. In this sense, the report presents the characterization through various techniques of three series of specimens where GaN was deposited on this ceramic composite, using different buffer layers, and a singular metal-organic chemical vapor deposition related technique for low temperature deposition. Other single crystalline ceramic-based templates were also utilized as substrate materials, for comparison purposes.

Low temperature growth of InAlN on epitaxially grown SiC/Si (111) wafers

Deposition of InAlN on commercially purchased SiC/(111) Si wafers has been performed in a temperature range of 530°C to 420°C using an alternating precursor MOCVD growth technique. The effect of an InN buffering layer between the substrate and the InAlN layer was explored. Varying the ratio between the InN and AlN in InAlN was also explored. Peak shifting to higher angles was observed in the InN interlayer with increasing AlN content. At temperatures of 510°C and above, indium metal can be seen desorb from the InAlN layer and form a (101) diffraction peak in measurements. Although aluminum can be seen to be present in the InAlN layers through EDX measurements, no indication of crystallinity can be observed through XRD at these temperatures.

Modeling of metal-oxide-semiconductor capacitor on Indium Gallium Nitride 1- channel model

A new analytical model for a two terminal metal-oxide-Gallium Nitride/Indium Gallium Nitride heterojunction structure is presented. This model characterizes the space charge layer created by electron tunneling in the structures channel which is made of intrinsic Gallium Nitride. A one dimensional (1-D) analysis is adopted, and a set of hypotheses is stated to frame the present work.

Structure of Isolated Oxygen Impurity States in InN

The electron state structure of isolated interstitial O atoms in real InN (containing clusters of InN, clusters of InON and clusters of non-stoichiometric InN:In) is the subject of investigation in this paper. It is shown that for the interstitial O atoms the corresponding symmetry is equivalent to that of an O atom in vacuum if the dielectric permittivity of InN is considered, and therefore the hydrogen like impurity atom analysis can be applied for isolated interstitial O atoms hosted in a real InN lattice. It is found that: i) If the O atom is interstitially incorporated in a cluster of pure InN the impurity state has an energy of -5.11 eV, which acts as a donor level with ionization energy +0.06 eV, and also this state is a donor level with an ionization energy of -0.02 eV for a cluster of InON if this cluster occurs at a distance of less than 30 Angstroms; ii) The impurity state has energy -5.15 eV if the O atom is interstitially incorporated in a cluster of InON, which acts as a donor level with ionization energy +0.02 eV, and also this state is a donor level with ionization energy +0.10 eV for a cluster of InN if this cluster occurs on a distance less than 60 Angstroms from the O atom. iii) If the O atom is interstitially incorporated in cluster of non-stoichiometric InN:In the impurity state has energy -5.38 eV, which is in the valence band of this cluster. However this state acts as donor level for both cluster of InN and cluster of InON if they are on distance less that 59 Angstroms from the O atom. The donor ionization energy for the first cluster is +0.33 eV, and for the second cluster it is +0.25 eV.

Field Effect Transistor on Hetero-Structure GaN/InxGa1-xN

Progress in the design of field effect transistor on hetero-structure GaN/InxGa1-xN is reported in this paper. The transistor uses new principle for modulation of the channel conductivity based on tunnel injection of electrons or holes through hetero-junction. The vertical GaN/InxGa1-xN hetero-structure is prepared to have both thickness ~50 mum and high specific resistance. The horizontal FET structure is prepared in order to achieve 1 mum gate length and 17 mum gate width. The technological methods used in the preparation of the FET structure are described. The static current-voltage characteristics are determined. It is found that there is gate threshold voltage that varies in range 2.1-2.4 V for n-channel MOS and in range -3.3--3.4 V for p-channel MOS . Also it is found that the drain current varies in the range ~7 muA if the drain voltage is 5 V and the operational point is chosen to be 3.5 V of the gate voltage. Both parameters the dynamic channel resistance and the amplification factor are determined as well