Band gap bowing, structural relaxations, and energies of formation were calculated for the three pseudobinary nitride zincblende alloy systems Al-Ga, In-Ga and In-Al using the full-potential linearized muffin-tin orbital method. The cluster expansion and Connolly-Williams approaches were used to relate calculated band structures and energies of formation of ordered compounds to the behavior of disordered alloys. Effects of bond length and volume variation on those properties are discussed. An interpolation formula for the gap of the full pseudoternary AlxGayInzN system is proposed and tested by separate calculations. Extension of the results to the wurtzite alloys is discussed.

Calculations of shallow donor states for wurtzite and zincblende structure GaN, and acceptor states for zincblende GaN in an effective mass approximation are presented. Band parameters were taken from experiment or determined from band structure calculations. The effect of wavevector dependent screening is examined, based on dielectric functions calculated from empirical pseudopotential band structures. For donor states, the effects of electron-phonon coupling and free carrier screening in the Thomas-Fermi and Debye approximations are discussed briefly.

Molecular dynamics simulations are employed to study defects in GaN. We use local basis density functional theory within the local density approximation where charge transfer between the ions is included in an approximate fashion. We find good agreement for the band structure of wurtzite and zincblende GaN compared to other recent calculations, suggesting the suitability of our method to describe GaN. A 96 atom GaN supercell is used to study the relaxations and electronic properties of common defects in the crystal structure, including Ga and N vacancies and antisites. We analyze the electronic signatures of these defects.

A probable byproduct of growth of crystalline GaN is an amorphous phase of the material. In this paper, we propose a structural model of amorphous GaN obtained from ah initio molecular dynamics. The radial distribution function, local bonding, electronic density of states and vibrational spectra are described. The network we obtain is highly disordered but exhibits a large state-free optical gap, and has no wrong (homopolar) bonds. These predictions are intended to elucidate the experimental signatures of amorphous GaN.

We present an ab-initio calculation of GaN wurtzite (1010) and zinc-blende (110) surface structures and formation energies. Our method employs ultrasoft pseudopotentials and plane-wave basis. These features enable us to obtain accurate results using small energy cut-off and large supercells. The (110) surface shows a Ga-N surface dimer rotation of ∼ 14°, i.e. about one half that of the ordinary III–V non-nitride compounds, and a 5% contraction of the surface bond-length (more than the double that occurring in GaAs). For the (1010) surface, a layer rotation angle of about 11° and a bond-length contraction of 6% has been found. Zinc-blende GaAs (110) and wurtzite ZnO (1010) surfaces have been studied as well, for the sake of comparison. GaAs results are in good agreement with the experimental findings. For ZnO a large bond contraction and a rotation angle of around 11% result. Thus, our findings place GaN closer in behaviour to the highly ionic II–VI compounds than to the non-nitride III–V semiconductors.

The formation and properties of acceptor-hydrogen pairs in GaN have been studied using radioactive 111mCd acceptors and the perturbed γγ angular correlation spectroscopy (PAC). After H-loading by low energy implantation (100 eV) at temperatures between 295 K and 473 K, the formation of two Cd-H complexes involving about 30% of the Cd-acceptors is observed. The complexes have been identified as single hydrogen atoms bound to the Cd acceptor in two different configurations. The dissociation enthalpies of these configurations have been determined as 1.1(1) eV and 1.8(1) eV, respectively.

The wide band gap group-III nitride materials continue to generate interest in the semiconductor community with the fabrication of green, blue, and ultraviolet light emitting diodes (LEDs), blue lasers, and high temperature transistors. Realization of more advanced devices requires pattern transfer processes which are well controlled, smooth, highly anisotropic and have etch rates exceeding 0.5 μm/min. The utilization of high-density chlorine-based plasmas including electron cyclotron resonance (ECR) and inductively coupled plasma (ICP) systems has resulted in improved etch quality of the group-III nitrides over more conventional reactive ion etch (RIE) systems.

Ion implantation doping and isolation is expected to play an enabling role for the realization of advanced Ill-Nitride based devices. In fact, implantation has already been used to demonstrate n- and p-type doping of GaN with Si and Mg or Ca, respectively, as well as to fabricate the first GaN junction field effect transistor.1-4 Although these initial implantation studies demonstrated the feasibility of this technique for the Ill-Nitride materials, further work is needed to realize its full potential.

After reviewing some of the initial studies in this field, we present new results for improved annealing sequences and defect studies in GaN. First, sputtered A1N is shown by electrical characterization of Schottky and Ohmic contacts to be an effective encapsulant of GaN during the 1100 °C implant activation anneal. The A1N suppresses N-loss from the GaN surface and the formation of a degenerate n+-surface region that would prohibit Schottky barrier formation after the implant activation anneal. Second, we examine the nature of the defect generation and annealing sequence following implantation using both Rutherford Backscattering (RBS) and Hall characterization. We show that for a Si-dose of l × l016 cm-2 50% electrical donor activation is achieved despite a significant amount of residual implantation-induced damage in the material.

The apparent thermal stability of hydrogen passivated Mg acceptors in GaN is a function of the annealing ambient employed, with H2 leading to a reactivation temperature approximately 150°C higher than N2. The dissociation of Mg-H complexes and the loss of hydrogen from GaN are sequential processes, with reactivation occurring at ≤700°C for annealing under N2, while significant concentrations of hydrogen remain in the crystal even at 900°C in implanted samples. The hydrogen is gettered to regions of highest defect density such as the InGaN layer in a GaN/InGaN double heterostructure. The addition of an accelerating potential for 2H+ ions in the plasma did not greatly affect the deuterium profiles.

Hydrogenated aluminum nitride (A1N:H) films have been deposited on the (100) silicon wafers by the RF reactive magnetron sputtering method with H2 gas in addition to an Ar-N2 gas mixture. Stoichiometric A1N films without oxygen impurities can be prepared by adding 10 % H2 to reactive gas, which is proven by Rutherford Backscattering Spectrometry (RBS). The bonding aspects of Al, N, O and H atoms in A1N:H films have been examined by X-ray Photoelectron Spectroscopy (XPS) and Fourier Transform Infrared (FTIR) to understand the effects of H2 addition. The chemical shift of the binding energies of A1, N and O atoms in A1N:H films from XPS analysis and the change of N-H bonding in FTIR with respect to different partial pressures of H2 gas have been confirmed. The role of H atoms is suggested to facilitate bonding with unbound N atoms in A1N:H films and hinder N-O bonding, thus, reducing oxygen concentration in A1N:H films. Also, the activation energy for the evolution of H2 gas from A1N:H film has been determined to be 0.11 eV/atom through a Kissinger-type analysis by a thermal desorption test using Gas Chromatograph(GC). This result implies that the hydrogen atom in film forms the hydrogen bond.

Indium droplet formation during the epitaxial growth of InxGa1-xN films is a serious problem for achieving high quality films with high indium mole fraction. In this paper, we studied the formation of indium droplets on the InxGa1-xN films grown by metalorganic chemical vapor deposition (MOCVD) using single crystal x-ray diffraction. It is found that the indium (101) peak in the x-ray diffraction spectra can be utilized as a quantitative measure to determine the amounts of indium droplets on the film. It is shown by monitoring the indium diffraction peak that the density of indium droplets increases at lower growth temperature. To suppress these indium droplets, a modulation growth technique is used. Indium droplet formation in the modulation growth is investigated and it is revealed in our study that the indium droplets problem has been partially relieved by the modulation growth technique.

A KrF (248 nm) excimer laser with a 38 ns pulse width was used to study pulsed laser annealing of AIN/GaN bi-layers and dopant activation of Mg-implanted GaN thin films. For the AIN/GaN bi-layers, cathodoluminescence (CL) showed an increase in the intensity of the GaN band-edge peak at 3.47 eV after pulsed laser annealing at an energy density of 2000 mJ/cm2. Rutherford backscattering spectrometry of a Mg-implanted A1N (75 nm thick)/GaN (1.0 μm thick) thin-film heterostructure showed a 20% reduction of the 4He+ backscattering yield after laser annealing at an energy density of 400 mJ/cm2. CL measurements revealed a 410 nm emission peak indicating the incorporation of Mg after laser processing.

Wet chemical etching of A1N and InxAl1-xN was investigated in KOH-based solutions as a function of etch temperature, and material quality. The etch rates for both materials increased with increasing etch temperatures, which was varied from 20 °C to 80 °C. The crystal quality of A1N prepared by reactive sputtering was improved by rapid thermal annealing at temperatures to 1100 °C with a decreased wet etch rate of the material measured with increasing anneal temperature. The etch rate decreased approximately an order of magnitude at 80 °C etch temperature after a 1100 °C anneal. The etch rate for In0.19Al0.81N grown by Metal Organic Molecular Beam Epitaxy was approximately three times higher for material on Si than on GaAs. This corresponds to the superior crystalline quality of the material grown on GaAs. Etching of InxAl1-xN was also examined as a function of In composition. The etch rate initially increased as the In composition changed from 0 to 36%, and then decreased to 0 Å/min for InN. The activation energy for these etches is very low, 2.0 ± 0.5 kcal•mol-1 for the sputtered A1N. The activation energies for InAIN were dependent on In composition and were in the range 2–6 kcal mol-1. GaN and InN layers did not show any etching in KOH at temperatures up to 80 °C.

ICl/Ar ECR discharges provide the fastest dry etch rates reported for GaN, 1.3 µm/min. These rates are much higher than with Cl2/Ar, CH4/H2/Ar or other plasma chemistries. InN etch rates up to 1.15 µm/min and 0.7 µm/min for In0.5Ga0.5N are obtained, with selectivities up to 5 with no preferential loss of N at low rf powers and no significant residues remaining. The rates are much lower with IBr/Ar, ranging from 0.15 µm/min for GaN to 0.3 µm/min for InN. There is little dependence on microwave power for either chemistry because of the weakly bound nature of IC1 and IBr. In all cases the etch rates are limited by the initial bond breaking that must precede etch product formation and there is a good correlation between materials bond energy and etch rate. The fact that low microwave power can be employed is beneficial from the viewpoint that photoresist masks are stable under these conditions, and there is no need for use of silicon nitride or silicon dioxide. Selectivities for GaN over A1N with IC1 and IBr are still lower than with Cl2- only.

A dry etch technique using Cl2 based reactive ion beam etching (RIBE) has been developd for GaN-based semiconductor lasers. The etching rate of 350 − 1000 Å/min was obtained. This is applicable for micro fabrication of GaN based materials in the same way as used for other III-V group semiconductors. Furthermore, it is found that the surface damage of GaN layers induced by the RIBE-etch can be removed using ultra-violet assisted wet-etching using alkali solution. The PL intensity of damaged GaN layers is increased after the post-process wet-etching.

In this paper, the first study of photo-assisted anodic etching of unintentionally doped n-GaN at room temperature is reported. The electrolyte used is a mixture of buffered aqueous solution of tartaric acid and ethylene glycol. The etching rate varies from ∼20 Å/min to as high as 1600 Å/min. A systematic study shows that i) the etch rate, as well as the surface roughness, increases with the current density; ii) the etching rate is the highest when the pH of the electrolyte is around 7; iii) the etching is faster when there is more ethylene glycol in the electrolyte solution.

LiGaO2 and LiAlO2 have similar lattice constants to GaN, and may prove useful as substrates for III-nitride epitaxy. We have found that these materials may be wet chemically etched in a number of acid solutions, including HF, at rates between 150–40,000 Å/min. Dry etching with SF6/Ar plasmas provides faster rates than Cl2/Ar or CH4/H2/Ar under Electron Cyclotron Resonance conditions, indicating the fluoride etch products are more volatile that their chloride or metalorganic/hydride counterparts. Dry etch rates are low ( < 2, 000 Å/min), providing high selectivity (>5) over the nitrides. The incorporation of hydrogen in these materials is also of interest because this could provide a reservoir of hydrogen that may passivate dopants in overlying nitride films. In 2H implanted samples, 50 % of the deuterium is lost by evolution from the surface by annealing at 400 °C for 20 min and all of the deuterium is gone at 700°C. The diffusivity of 2H is ∼10-13 cm2/s at 250°C in LiA1O2, approximately two orders of magnitude higher than in LiGaO2.

The development of reliable Ohmic and Schottky contacts on GaN will require an understanding of the thermal stability and metallurgy of metal-GaN contact structures. We investigated the behavior of Pt, Pd, and Ni on GaN as a function of annealing temperature. Rutherford backscattering spectrometry, x-ray diffraction, and scanning electron microscopy were used to characterize the interface and surface behavior. 800Å thin metal films were deposited by sputtering on 2μm GaN films grown by metal organic chemical vapor deposition on sapphire substrates. No reactions occur in the Pt, Pd, and Ni systems with annealing up to 800°C. The Pt film begins to form submicron spheres and islands after annealing above 600°C. The Pd and Ni films begin to island with annealing above 700°C. Below these temperatures no structural changes were observed.

The formation of n-GaN/Ti ohmic contacts with TiN diffusion barriers has been investigated by electrical measurements, x-ray diffraction and SIMS. It has been shown that the onset of the ohmic behaviour is associated with the thermally induced phase transformation of Ti into TiN at the GaN/Ti interface. It is suggested that the process is accompanied by an increase in the doping level in the semiconductor subcontact region. The presence of a TiN barrier is found to inhibit excessive decomposition of GaN and to confine the reaction between n-GaN and Ti.

We report new Cr/Ni/Au and Ni/Cr/Au tri-layer metallization schemes for achieving low resistance ohmic contacts to moderately doped p- (∼1 × 1017/cm3), and n-GaN (∼1 × 1018/cm3) respectively. The metallizations were thermally evaporated on 2 μm-thick GaN layers grown on c-plane sapphire substrates by metalorganic chemical vapor deposition (MOCVD). Comparisons with bi-layer metallizations such as Ni/Au and Cr/Au were also made. The Cr/Ni/Au contacts showed a low specific contact resistivity of 9.1 × 10−5 Ω⋅cm2 to n-GaN while that of Ni/Cr/Au to p-GaN was 8.3 × 10−2 Ω⋅cm2. The Ni/Cr/Au contacts also showed a low specific contact resistivity of 2.6 × 10−4 Ω⋅cm2 to n-GaN. The Ni/Cr/Au metallization could made reasonable ohmic contacts to p- and n-GaN simultaneously