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Polarization doping in a GaN-InN system with a graded composition layer was studied using ab initio simulations. The electric charge volume density in the graded concentration part was determined by spatial potential dependence. The emerging graded polarization charge was determined to show that it could be obtained from a polarization difference and the concentration slope. It was shown that the GaN-InN polarization difference is changed by piezoelectric effects. The polarization difference is in agreement with the earlier obtained data despite the relatively narrow bandgap for the simulated system. The hole generation may be applied in the design of blue and green laser and light-emitting diodes.

In this work, we study the emergence of polarization doping in AlxGa1-xN layers with graded composition from a theoretical viewpoint. We demonstrate that the charge conservation law applies for fixed and mobile charges separately, leading to nonlocal compensation phenomena involving bulk fixed and mobile charge and polarization sheet charge at the heterointerfaces. The magnitude of the effect allows obtaining technically viable mobile charge density for optoelectronic devices without impurity doping (donors or acceptors). Therefore, it provides an additional tool for the device designer, with the potential to attain high conductivities: high carrier concentrations can be obtained even in materials with high dopant ionization energies, and the mobility is not limited by scattering at ionized impurities., Comment: 16 pages, 4 figures

To improve the properties of semiconductors, it is necessary to construct an integrated crystal growth model that covers all elementary processes of metal–organic vapor phase epitaxy (MOVPE). Altho...

An ab initio-based approach is used to investigate the facet stability of GaN during tri-halide vapor phase epitaxy (THVPE). First, surface reconstructions are analyzed to create surface phase diagrams as a function of the gaseous pressure and temperature. Next, a triangular wedge model is used to compute absolute surface formation energies with the bulk state as a reference. A Wulff construction is used to predict the crystal growth form composed of energetically preferred facets. The calculated results can be used to control the shape of GaN grown by THVPE.

Immiscible semiconductors are of premier importance since the source of lighting has been replaced by white light-emitting-diodes (LEDs) composed of thermodynamically immiscible InxGa1−xN blue LEDs and yellow phosphors. For realizing versatile deep-ultraviolet to near-infrared light-emitters, Al1−xInxN alloys are one of the desirable candidates. Here we exemplify the appearance and self-formation sequence of compositional superlattices in compressively strained m-plane Al1−xInxN films. On each terrace of atomically-flat m-plane GaN, In- and Al-species diffuse toward a monolayer (ML) step edge, and the first and second uppermost $$\stackrel{-}{1}\stackrel{-}{1}20$$ 1 - 1 - 20 > cation-rows are preferentially occupied by Al and In atoms, respectively, because the configuration of one In-N and two Al-N bonds is more stable than that of one Al-N and two In-N bonds. Subsequent coverage by next $$\stackrel{-}{1}\stackrel{-}{1}20$$ 1 - 1 - 20 > Al-row buries the $$\stackrel{-}{1}\stackrel{-}{1}20$$ 1 - 1 - 20 > In-row, producing nearly Al0.5In0.5N cation-stripe ordering along [0001]-axis on GaN. At the second Al0.72In0.28N layer, this ordinality suddenly lessens but In-rich and In-poor $$\stackrel{-}{1}\stackrel{-}{1}20$$ 1 - 1 - 20 >-rows are alternately formed, which grow into respective {0001}-planes. Simultaneously, approximately 5-nm-period Al0.70In0.30N/Al0.74In0.26N ordering is formed to mitigate the lattice mismatch along [0001], which grow into approximately 5-nm-period Al0.70In0.30N/Al0.74In0.26N {$$10\stackrel{-}{1}2$$ 10 1 - 2 } superlattices as step-flow growth progresses. Spatially resolved cathodoluminescence spectra identify the emissions from particular structures.

Based on the density functional theory (DFT), we theoretically investigate the growth mechanism of GaN (0001) using the Metal-Organic Vapor-Phase Epitaxy (MOVPE). We first identify the structure of the growing Ga rich GaN (0001) surface, then study the adsorption of NH x (x = 0–3) on such surface. We find that NH 2 and NH units spontaneously intervene in the Ga-Ga weak bonds on the Ga-rich GaN (0001) surface. A reaction pathway of decomposition of NH 3 on Ga rich surface is revealed. During reaction, N is found to incorporate in the weak Ga-Ga bond and form – Ga – (NH) – Ga – structure. The activation barrier of NH 3 is surprisingly small, just 0.63 eV. We also explore the decomposition of NH 2 to N to form Ga-N network and find the plausible reaction pathway with the energy barrier of 2 eV. Taking into account the chemical potential of an H 2 molecule in the gas phase at the growth temperature, we find that this reaction can be overcome. This NH 3 decomposition mechanism and the N incorporation on GaN is a new growth mechanism catalyzed by the growing surface.

III-Nitride semiconductors are attractive materials for optoelectronic devices including LEDs and LDs. To enhance the device performances, it is important to prevent impurity incorporation during thin film growth. The knowledge of atomistic-scale phenomena is indispensable to prevent contamination of thin films. In the present work, we model elementary growth processes in GaN MOVPE such as (1) vapor phase reaction, (2) surface reaction and (3) solid-phase diffusion during epitaxy. In this presentation, we discuss incorporation mechanisms of carbon in GaN(0001) and (000-1) MOVPE, and of oxygen in vicinal GaN(10-10) MOVPE.

International audience; We report first-principles calculations based on the density-functional theory that clarify atomic reactions of ammonia decomposition and subsequent nitrogen incorporation during GaN epitaxial growth. We find that Ga-Ga weak bonds are ubiquitous on Ga-rich growing surface and responsible for the growth reactions. Furthermore, Car-Parrinello Molecular Dynamics simulations predict the existence of 2-dimensional Ga liquid phase, providing new insight into the epitaxial growth. The obtained results are expected to become basics for multiscale growth simulations in future.

We report density functional calculations that clarify atom-scale mechanisms of vapor-phase epitaxial growth of GaN with gas sources of trimethylgallium and ammonia. We identify various stable adsorption structures of a Ga atom and NHx molecules (x = 0–3) on GaN(0001) surfaces and find that NH2 and NH units spontaneously intervene in Ga–Ga surface bonds on Ga-rich GaN(0001) surface. We then explore the reaction in which NH3 on the surface is decomposed and becomes an N-incorporated structure, −Ga–(NH)–Ga–, on the Ga-rich GaN(0001) and find that the reaction occurs with the energy barrier of 0.63 eV. Further exploration reveals that a reaction of H2 desorption occurs with the energy barrier of 2 eV, leaving the N atom incorporated in the Ga–N network. This barrier can be overcome when we consider the chemical potential of an H2 molecule in the gas phase at the growth temperature. This N incorporation on GaN is a new growth mechanism catalyzed by the growing surface.

Adsorption of atomic and molecular nitrogen at AlN(000–1) surface was investigated by ab initio calculations and thermodynamic analysis. According to earlier works{Kempisty et al. Appl. Surf. Sci. 2020, 532, 147,719} in equilibrium with Al vapor, the AlN(000–1) surface is thermodynamically stable in two states: low Al coverage θAl ≤ 1/3 ML and high Al coverageθAl ≅ 1 ML. In these two cases nitrogen adsorption is completely different. At low Al-covered surface the nitrogen atom is strongly bounded to N surface atom, creates the N2 admolecule that is finally detached leaving surface vacancy VN(s). This reaction chain energy gain is positive, Δ E D F T d e t ( N − N 2 ) = 3.50 e V . Therefore, the atomic nitrogen present in plasma assisted molecular beam epitaxy (PA-MBE) fluxes induces the surface decay. N2 is adsorbed molecularly at the bare surface with the coverage independent energy gain about 1 eV. At the fully Al-covered surface atomic nitrogen is adsorbed in T4 sites with no barrier and large energy gain Δ E D F T a d s − A l ( N ) = 8.68 e V . Molecular nitrogen dissociates with the energy gain, dependent on additional N coverage: Δ E D F T a d s − A l ( N 2 ) = 7.65 e V at low and Δ E D F T a d s − A l ( N 2 ) = 2.77 e V at high, respectively. This change is related to the reduction of electron transfer contribution, caused by Fermi level shift down due to electron transfer from Al to N surface states. The thermodynamic analysis shows incomplete N coverage above the adsorbed Al layer due to the above adsorption energy reduction effect. The resulting incomplete N coverage is responsible for creation of nitrogen vacancies during AlN physical vapor transport (PVT) growth and their coalescence into Al-rich inclusions.

The III-nitride semiconductors, GaN, AlN and InN, have direct bandgaps and the bandgaps of their alloys can cover a wide range. Therefore, they are widely used as materials for optical devices. Moreover, they have received considerable attention as materials for future high performance power devices [1,2]. To develop these devices, it is crucial to fabricate high-quality GaN crystals by epitaxial growth. For their epitaxial growth, metal organic vapor phase epitaxy (MOVPE) is generally used. In GaN, AlN and InN MOVPE, trimethylgallium (TMG), trimethylaluminum (TMA) and trimethylindium (TMI) are used for the group III sources, respectively. NH3 is used for the nitride source, and H2 and N2are used as carrier gases. In MOVPE, TMG, TMA and TMI should decompose into gas phase Ga, Al and In atoms, respectively. The chemical equation can be written as Ga(CH3)3(g) + 3/2 H2(g) → Ga(g) + 3CH4(g) There are many studies which have investigated their decomposition reactions[3,4]. However, the details have not been clarified and also many problems have been reported from experiments. In the case of GaN MOVPE, the gas phase reaction for the formation of the (CH3)2GaNH2 adduct has been reported [5,6], and these authors believe that GaN nanoparticles were formed from the (CH3)2GaNH2adduct in the gas phase reaction near the surface. On the other hand, it is also thought that Ga is incorporated as gas phase Ga atoms on the GaN growth surface and that these migrate along the surface [7,8]. In this paper, we carry out a theoretical investigation of the MOVPE growth processes of GaN and present a theoretical discussion of the decomposition processes of the source gases. In this study, we performed first-principles calculations and thermodynamic analyses to investigate the reaction processes of TMG and whether the (CH3)2GaNH2, adducts can be formed in the gas phase reaction during MOVPE [9]. We investigated the decomposition process of TMG for GaN MOVPE. In this presentation, we discuss the reactions by which TMG with H2 decomposes into dimethylgallium (DMG, [Ga(CH3)2]), monomethylgallium (MMG, [Ga(CH3)]), and gas phase Ga atoms and the reaction by which TMG with NH3 forms the (CH3)2GaNH2adduct. The reaction formulas can be written as follows. (a) Ga(CH3)3(g) + H2(g) → Ga(CH3)2(g) + CH4(g) (b) Ga(CH3)3(g) + H2(g) → Ga(CH3)(g) + 2CH4(g) (c) Ga(CH3)3(g) + H2(g) → Ga(g) + 3CH4(g) (d) Ga(CH3)3(g) + NH3(g) → (CH3)2GaNH2(g) + CH4(g) Fig. 1 shows ΔG for the above four reactions. The calculations show that ΔG for reaction (d), through which TMG forms the (CH3)2GaNH2 adduct, is negative at any temperature and has the lowest value of the four reactions between 0 K and 280 K. That is, TMG reacts with NH3 and forms the (CH3)2GaNH2 adduct in this temperature range. Moreover, in reaction (b) TMG decomposing into MMG is the easiest reaction occurring between 280 and 570 K, and in reaction (c) TMG decomposing into gas phase Ga atoms is the easiest occurring above 570 K. Considering the substrate temperature of 1300 K, almost all the TMG decomposes into gas phase Ga atoms and the Ga atoms migrate on the GaN growth surfaces. TMG hardly reacts with NH3 and the formation of the (CH3)2GaNH2 adduct cannot occur, although there have been reports which claim that the (CH3)2GaNH2adduct forms [5,6]. 1. Stephen K. O’Leary, Brian E. Foutz, Michael S. Shur, and Lester F. Eastman, J Mater Sci: Mater Electron 17, 87 (2006). 2. G. Martin, A. Botchkarev, A. Rockett, and H. Morkoc, Appl. Phys. Lett. 68, 2541 (1996). 3. Y. S, Hiraoka and M. Mashita, J. Cryst. Growth 136, 94 (1994). 4. S. H. Kim, H. S. Kim, J. S. Hwang, J. G. Choi, and P. J. Chong, J. Chem. Mater. 6, 278 (1994). 5. D. Sengupta, S. Mazumder, W. Kuykendall, and S. A. Lowry, J. Cryst. Growth 279, 369 (2005). 6. A. Thon and T. F. Kuech, Appl. Phys. Lett. 69, 55 (1996). 7. Y. Kangawa, T. Akiyama, T. Ito, K. Shiraishi, and T. Nakayama, Materials 6, 3309 (2013). 8. Y. Kangawa, T. Akiyama, T. Ito, K. Shiraishi, and T. Kakimoto, J. Cryst. Growth 311, 3106 (2009). 9. K. Sekiguchi, H. Shirakawa, K. Chokawa, M. Araidai, Y. Kangawa, K. Kakimoto, and K. Shiraishi, Jpn. J. Appl. Phys. 56, 04CJ04 (2017) Figure 1

We analyzed the decomposition mechanisms of trimethylgallium (TMG) used for the gallium source of GaN fabrication based on first-principles calculations and thermodynamic analysis. We considered two conditions. One condition is under the total pressure of 1 atm and the other one is under metal organic vapor phase epitaxy (MOVPE) growth of GaN. Our calculated results show that H2 is indispensable for TMG decomposition under both conditions. In GaN MOVPE, TMG with H2 spontaneously decomposes into Ga(CH3) and Ga(CH3) decomposes into Ga atom gas when temperature is higher than 440 K. From these calculations, we confirmed that TMG surely becomes Ga atom gas near the GaN substrate surfaces.

Using ab initio calculations, a simple model for GaAs1-xNx vapor-phase epitaxy on (100) surface of GaAs was created. By studying As2 and H2 molecules adsorptions and As/N atom substitutions on (100) GaAs surfaces, we obtain a relative stability diagram of all stable surfaces under varying As2, H2, and N2 conditions. We previously proved that this model could describe the vapor-phase epitaxy of GaAs1-x Nx with simple, fully decomposed, precursors. In this paper, we show that in more complex reaction conditions using monomethylhydrazine (MMHy), and dimethylhydrazine (DMHy), it is still possible to use our model to obtain an accurate description of the temperature and pressure stability domains for each surfaces, linked to chemical beam epitaxy (CBE) growth conditions. Moreover, the different N-incorporation regimes observed experimentally at different temperature can be explain and predict by our model. The use of MMHy and DMHy precursors can also be rationalized. Our model should then help to better understand the conditions needed to obtain an high quality GaAs1-xNx using vapor-phase epitaxy.

In this paper, we present systematic improvements to a method that allows us to determine the surface phase diagrams based on ab initio calculations and atomistic thermodynamics. In particular, we include a contribution derived from thermal vibrations of the surface, which is usually omitted in such analysis. On the basis of first-principles phonon calculations, we determine a zero-point vibrational energy and thermal dependencies of vibrational entropy and free energy for atoms and molecules adsorbed on the surface. A series of polar GaN(0001) surfaces are examined. Significant changes are observed in the surface phase diagrams compared to the diagrams obtained by standard density-functional theory calculations without phononic contributions.

It is known that threading dislocations degrade the performance of GaN-based electronic devices. Electronic structure of threading dislocations in GaN is not fully understood. Accordingly, we examine the electronic structures of threading dislocations in GaN using first principles calculations based on density functional theory (DFT) and to clarify the origin of the leakage current. We have comprehensively studied the relation between threading core structures and electronic property in GaN thin films. Our calculation models of threading dislocations are the edge dislocations with Burgers vectors of 1/3 [11-20] and the screw dislocations with Burgers vectors of [0001]. We examined various core types of the threading dislocations. We found that both edge dislocations and screw dislocations do not cause the leakage currents in n-type GaN based devices because no defect level appears near the conduction band bottom.

We investigate the decomposition process of trimethylgallium (TMGa) during GaN metal organic vapor phase epitaxy in detail by using ab inito calculations. We analyze the decomposition rate of TMGa by estimating Gibbs energy of activation including H2 as well as NH3 effects. Our obtained main reaction pathway of TMGa decomposition is as follows: Ga(CH3)3 + 3H2 + NH3 → Ga(CH3)2NH2 + 3H2 + CH4 → Ga(CH3)2H + 2H2 + NH3 +CH4 → GaCH3HNH2 + 2H2 + 2CH4 → GaCH3H2 + H2 + NH3 + 2CH4 → GaH2NH2 + H2 + 3CH4 → GaH3 + NH3 + 3CH4. Our proposed TMGa decomposition pathway can represent the actual epitaxial growth phenomenon by considering neither polymerization reactions nor radical reactions, which are now widely adopted in fluid simulations of crystal growth. Moreover, our proposed pathway is in good agreement with the experiments.

The role of bond creation and electron transition contribution were investigated in thermodynamic picture of adsorption obtained from intensive ab initio density functional theory (DFT) calculations. It was shown that electron transitions may reduce the overall energy gain from Al adsorption at AlN(000 1 ) surface by 50%. Accordingly properties of AlN polar N-terminated AlN(000 1 ) surface such as crystallographic structure, the type and energy of the surface states, the band profiles close to the surface were obtained. At the clean surface Al is adsorbed with the energy gain of 9.6 eV at H3 site creating bonds using two Al3p states by the overlap with the neighboring surface N atoms. The excess electrons are transferred to surface N broken bond states. At the critical coverage θ Al - c r = 1 4 M L all these states are occupied, therefore for higher Al coverage the electrons are transferred to Al3pz states. As their energy is higher by 2.5 eV, the adsorption energy gain is dropped to 4.089 eV, i.e. about 50%. For higher coverage Al adatoms are shifted to bridge and on-top configurations reducing the electron transfer and increasing energy gain by 2.5 eV for full coverage of Al adatoms located in the on-top positions. The temperature dependent pressure-coverage diagram was obtained showing the two stable regions. The first, up to 0.25 ML Al ( θ Al ≤ 1 4 M L ) with Al adatoms located in H3 positions, correspond to extremely low Al pressure, below 10−13 bar at 2500 K. The second region, at p Al > 2.18 × 10 - 5 b a r , is stable for high coverage, i.e. for θ Al > 0.999 M L (at 2500 K) with Al adatoms located in the on-top positions. For the pressures between, i.e. 1.80 × 10 - 12 b a r p Al 2.18 × 10 - 5 b a r , nonuniform coverage is stable, composed to these two phases. Finally at the coverage close to 1 ML, Langmuir entropic singularity in chemical potential was detected, corresponding to dramatic increase of the pressure over single Al layer which leads to transition to multiple Al layers and bulk Al.

Absolute surface energies of reconstructed polar, nonpolar, and semi-polar GaN surfaces formed under oxide vapor phase epitaxy (OVPE) growth conditions were investigated via first-principles calculations. The relationships of stable surface orientations and surface structures with the growth conditions of Ga pressure and temperature were examined in terms of absolute surface energies. The stability of the surface orientation was in the order (0 0 0 1 ¯ ), (1 1 ¯ 0 1), (1 1 ¯ 0 0), (1 1 2 ¯ 0), (0 0 0 1), and (1 1 ¯ 0 1 ¯ ). High O concentrations on OVPE-grown GaN could be explained in relation to the stability of the (1 1 ¯ 0 1) surface. The stable (1 1 ¯ 0 1) surface consisted of N vacancies and H and O adatoms. Therefore, it was deduced that its appearance results in increased O impurity incorporation.

Using density functional calculations, we clarify the oxygen incorporation mechanism in vicinal m-GaN growth by metal-organic vapor-phase epitaxy. We first identify reconstructed structures of 5° off m-GaN toward the ±c directions. Next, we explore preferable sites for oxygen substitution near step edges. We find that oxygen prefers the lower nitrogen site of the step edge on the +c 5° off m-GaN substrate compared with that on the –c 5° off m-GaN substrate. This tendency agrees with recent experimental findings that the oxygen concentration in −c 5° off m-GaN epilayers is lower than that in +c 5° off m-GaN epilayers.

GaN is a key material for realizing an energy saving society owing to its superior properties for power devises. Understanding the physics of the crystal growth can accelerate the development of GaN-based devices. There have been multiple theoretical studies that investigate the surface reconstructions with minimum energy from GaN during growth. However, although the most stable reconstruction is dominant on the surface, other reconstructions could also appear probabilistically due to the entropic effect. Considering the growth rate of GaN is typically limited by the Ga precursor flow rate, the appearance probability of Ga-adsorbed reconstruction should be small. Little is known about the relative stabilities of such minor reconstructions. Here, we propose a new scheme to calculate the appearance probabilities of reconstructions. Our calculation reveals that the N density increases and Ga density decreases on GaN(0 0 0 1) during metalorganic vapor phase epitaxy (MOVPE) with decreasing H2 partial pressure, resulting in a highly N-rich surface. In contrast, for GaN(0 0 0 −1), both N and Ga densities increase with decreasing H2 partial pressure, resulting in a Ga-rich surface. The results well explain the reported growth characteristics of polar GaN.

In this section, atomic arrangement and indium incorporation in InGaN epitaxial layers are discussed. Chichibu et al. have studied why In-containing (Al, In, Ga)N films exhibit a defect-insensitive emission probability.

In this chapter, influences of N/III ratio, growth orientation and total pressure on epitaxial growth processes of In(Ga)N are discussed. It is known that N/III ratio is essential parameter to grow In(Ga)N thin films.

GaAs(100) c(4×4) surfaces were examined by ab initio calculations, under As2, H2 and N2 gas mixed conditions as a model for GaAs 1 − x N x vapor-phase epitaxy (VPE) on GaAs(100). Using a simple model consisting of As2 and H2 molecules adsorptions and As/N atom substitutions, it was shown to be possible to examine the crystal growth behavior considering the relative stability of the resulting surfaces against the chemical potential of As2, H2 and N2 gases. Such simple model allows us to draw a picture of the temperature and pressure stability domains for each surfaces that can be linked to specific growth conditions, directly. We found that, using this simple model, it is possible to explain the different N-incorporation regimes observed experimentally at different temperatures, and to predict the transition temperature between these regimes. Additionally, a rational explanation of N-incorporation ratio for each of these regimes is provided. Our model should then lead to a better comprehension and control of the experimental conditions needed to realize a high quality VPE of GaAs 1 − x N x .

Clearly understanding elementary growth processes that depend on surface reconstruction is essential to controlling vapor-phase epitaxy more precisely. In this study, ammonia chemical adsorption on GaN(0001) reconstructed surfaces under metalorganic vapor phase epitaxy (MOVPE) conditions (3Ga-H and Nad-H + Ga-H on a 2 × 2 unit cell) is investigated using steepest-entropy-ascent quantum thermodynamics (SEAQT). SEAQT is a thermodynamic-ensemble based, first-principles framework that can predict the behavior of non-equilibrium processes, even those far from equilibrium where the state evolution is a combination of reversible and irreversible dynamics. SEAQT is an ideal choice to handle this problem on a first-principles basis since the chemical adsorption process starts from a highly non-equilibrium state. A result of the analysis shows that the probability of adsorption on 3Ga-H is significantly higher than that on Nad-H + Ga-H. Additionally, the growth temperature dependence of these adsorption probabilities and the temperature increase due to the heat of reaction is determined. The non-equilibrium thermodynamic modeling applied can lead to better control of the MOVPE process through the selection of preferable reconstructed surfaces. The modeling also demonstrates the efficacy of DFT-SEAQT coupling for determining detailed non-equilibrium process characteristics with a much smaller computational burden than would be entailed with mechanics-based, microscopic-mesoscopic approaches. Published version

Chemical vapor deposition has been developed to enable defect-free 4H-SiC crystals to be grown at lower cost and with higher growth rates. However, the structure and stability of 4H-SiC surfaces during crystal growth has not been clarified. In this study, we performed first-principles calculations and obtained the surface energies of ideal surfaces and Si-terminated surfaces on (0001), (000) and (100) surfaces. For the (0001) and (000) surfaces, the Si-terminated surfaces are more stable than the ideal surfaces and Si atoms are adsorbed onto the surfaces up to high temperatures. The ideal surface on the (100) surface is stable, and the Si-terminated surface changes to an ideal surface at lower temperatures than on the (0001) and (000) surfaces. These results indicate the possible temperature ranges in which to perform crystal growth. Thus, we clarified the conditions required to grow 4H-SiC crystals and the dependency of these structures on surface orientation.

We perform an improved method of thermodynamic analysis for semipolar 11 2 ¯ 2 and 1 1 ¯ 01 surfaces of GaN and AlN to elucidate the relationship between growth conditions and semipolar and polar surfaces during metalorganic vapor phase epitaxy (MOVPE). The calculations for H2 carrier gas suggest that for both GaN and AlN the maximum temperature for growth on 11 2 ¯ 2 surfaces is higher than that for growth on 0001 surfaces. On the other hand, the maximum temperature for growth on GaN 1 1 ¯ 01 surfaces is comparable to that for growth on GaN 0001 surfaces, while the maximum temperature for the growth on AlN 0001 surfaces is higher than that for growth on AlN 1 1 ¯ 01 surfaces. These results could be used to provide favorable conditions for growth of group-III nitrides along a semipolar orientation during MOVPE.

Suppression of carbon contamination in GaN films grown using metalorganic vapor phase epitaxy (MOVPE) is a crucial issue in its application to high power and high frequency electronic devices. To know how to reduce the C concentration in the films, a sequential analysis based on first principles calculations is performed. Thus, surface reconstruction and the adsorption of the CH4 produced by the decomposition of the Ga source, Ga(CH3)3, and its incorporation into the GaN sub-surface layers are investigated. In this sequential analysis, the dataset of the adsorption probability of CH4 on reconstructed surfaces is indispensable, as is the energy of the C impurity in the GaN sub-surface layers. The C adsorption probability is obtained based on steepest-entropy-ascent quantum thermodynamics (SEAQT). SEAQT is a thermodynamic ensemble-based, non-phenomenological framework that can predict the behavior of non-equilibrium processes, even those far from equilibrium. This framework is suitable especially when one studies the adsorption behavior of an impurity molecule because the conventional approach, the chemical potential control method, cannot be applied to a quantitative analysis for such a system. The proposed sequential model successfully explains the influence of the growth orientation, GaN(0001) and (000&minus, 1), on the incorporation of C into the film. This model can contribute to the suppression of the C contamination in GaN MOVPE.

We review the surface stability and growth kinetics of III-V and III-nitride semiconductors. The theoretical approach used in these studies is based on ab initio calculations and includes gas-phase free energy. With this method, we can investigate the influence of growth conditions, such as partial pressure and temperature, on the surface stability and growth kinetics. First, we examine the feasibility of this approach by comparing calculated surface phase diagrams of GaAs(001) with experimental results. In addition, the Ga diffusion length on GaAs(001) during molecular beam epitaxy is discussed. Next, this approach is systematically applied to the reconstruction, adsorption and incorporation on various nitride semiconductor surfaces. The calculated results for nitride semiconductor surface reconstructions with polar, nonpolar, and semipolar orientations suggest that adlayer reconstructions generally appear on the polar and the semipolar surfaces. However, the stable ideal surface without adsorption is found on the nonpolar surfaces because the ideal surface satisfies the electron counting rule. Finally, the stability of hydrogen and the incorporation mechanisms of Mg and C during metalorganic vapor phase epitaxy are discussed.

We studied dependence of process parameters, such as temperature of a seed, pressure in a furnace and surface polarity of a substrate, on polytypes of SiC in a process of physical vapor transport. The analysis was based on a classical thermodynamic nucleation theory in conjunction with numerical results obtained from a global model. We investigated which polytype was more stable in the nucleation stage by a comparison of nucleation energies of each polytype. The results show that the formation of 4H-SiC was more stable than that of 6H-SiC when we used C-face SiC as a seed. Furthermore, the most stable polytype could change from 4H-SiC to 6H-SiC in a condition of higher supersaturation, with a condition of higher temperature of a seed and lower pressure in a furnace. Meanwhile, the formation of 6H-SiC was more stable than 4H-SiC when Si-face of a seed was used.

In this study, we simulated the solution growth of gallium nitride (GaN) and investigated the diffusion behavior of nitrogen (N) atoms on growth surfaces by molecular dynamics simulation. The simulation showed that the Ga-face grew flatter than the N-face. Comparing the diffusion coefficients of a N atom on Ga- and N-faces, the values on the Ga-face were about 3.5 times larger than those on the N-face.

In this paper, we use thermodynamic analysis to determine how the nitrogen (N) ratio in the source gases affects the solid composition of coherently grown GaAs 1− x N x ( x ∼0.03). The source gases for Ga, As, and N are trimethylgallium ((CH 3 ) 3 Ga), arsine (AsH 3 ), and ammonia (NH 3 ), respectively. The growth occurs on a Ge substrate, and the analysis includes the stress from the substrate–crystal lattice mismatch. Calculation results indicate that to have just a few percent N incorporation into the grown solid, the V/III ratio in the source gases should be several thousands and the input-gas partial-pressure ratio NH 3 /(NH 3 +AsH 3 ) should exceed 0.99. We also find that the lattice mismatch stress from the Ge substrate increases the V/III source–gas ratio required for stable growth, whereas an increase in input Ga partial pressure ratio has the opposite effect.

To investigate the possibility of AlN synthesis from Li3N and Al as source materials, a phase diagram of the Li3N-Al system was constructed by using calculation of the phase diagram (CALPHAD) method. Thermodynamic data of a ternary system was prepared on the basis of data of binary systems, which are Al-Li, Al-N and Li-N. In the present work, we newly incorporated thermodynamic data of Li3AlN2 into the system. Gibbs energy function of Li3AlN2 is described by a stoichiometric compound model and the parameter was determined to reproduce our experimental results. The calculated phase diagram was verified by differential thermal analysis (DTA). The calculated solution temperature of Li3AlN2 agreed with the DTA results and the validity was confirmed. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)