We report the formation of p-type nitrogen doped ZnO (ZnO:N) grown by thermal-evaporation deposition. The effects of nitrogen precursors on the electrical and optical properties of ZnO:N were investigated. This study shows that growth process plays a critical role in the electrical properties of ZnO:N. The chemical reaction mechanism was analyzed.

Temperature-dependent Hall-effect measurements have been performed on three Ga-doped ZnO thin films of various thicknesses (65, 177, and 283 nm), grown by pulsed laser deposition at 400 °C and annealed at 400 °C for 10 min in Ar, N2, or forming-gas (5% H2 in Ar). The donor ND and acceptor NAconcentrations as a function of sample thickness and annealing conditions are determined by a new formalism that involves only ionized-impurity and boundary scattering. Before annealing, the samples are highly compensated, with ND = (2.8 ± 0.3) × 1020 cm-3 and NA = (2.6 ± 0.2) × 1020 cm-3. After annealing in Ar the samples are less compensated, with ND = (3.7 ± 0.1) × 1020 cm-3 and NA = (2.0 ± 0.1) × 1020 cm-3; furthermore, these quantities are nearly independent of thickness. However, after annealing in N2 and forming-gas, ND and NA are thickness dependent, partly due to depth-dependent diffusion of N2 and H, respectively.

In an effort to investigate the stability of the surface and hetero-interface of AlGaN/GaN HEMTs during high temperature device processing steps, AlGaN/GaN HEMT samples were subjected to temperatures from 650°C to 1150°C for a period of 30 seconds prior to processing. Hall and photoluminescence measurements were performed on samples before and after temperature stressing. The samples annealed at 700°C and 1150°C were then processed, and electrical parametric data were collected during and after processing. Large increases in HEMT Schottky gate diode reverse leakage current are observed at higher pre-process annealing temperatures, while the low-field mobility decreases.

We have studied the effects of hydrogen plasma treatment on the defect characteristics in single crystal ZnO grown at Eagle-Picher by chemical vapor transport. Depth-dependent cathodoluminescence (CL) spectra, temperature-dependent (9–300 K) and excitation intensity-dependent photoluminescence (PL) spectra reveal significant changes resulting from unannealed exposure of n-type ZnO to a remote hydrogen plasma. Low temperature PL spectra show that this hydrogen exposure effectively suppresses the free-exciton transition and redistributes intensities in the bound-exciton line set and two-electron satellites with their phonon replicas. The resultant spectra after hydrogenation exhibit a new peak feature at 3.366 eV possibly related to a neutral donor bound exciton. A simple thermal analysis of the activation energy for the 3.366 eV line yields 5–10 meV. Hydrogenation also produces a violet 100 meV-wide peak centered at 3.16 eV. Remote plasma hydrogenation produces similar changes in room-temperature CL spectra: near-band edge emission intensity increases with hydrogenation. Furthermore, this new emission increases with proximity to the free ZnO surfaces, i.e., with decreasing the energy of the incident electron beam from 3.0 down to 0.5 keV. Subsequent annealing at 450 °C completely restores both the PL and CL spectra in the sub-band gap range. The appearance of a new bound-exciton feature at 3.366 eV with H plasma exposure, the near-surface nature of the spectral changes, and the reversibility of spectral features with annealing indicate a direct link between H indiffusion and appearance of a shallow donor.

In this study, InN films with thickness up to 7.5 micron were prepared by molecular beam epitaxy (MBE) on (0001) sapphire and quasi-bulk GaN templates. Previously it has been challenging to grow InN film much beyond 1 micron because the growing surface tended to become rough. Techniques to overcome this limit have been developed. Various buffer techniques were used and compared to optimize the epitaxial growth. It was found that with increasing film thickness, Hall mobility will monotonically increase, while carrier concentration decreases. Hall mobility beyond 2100 cm2/Vs with carrier concentration close to 3×1017 cm−3 was obtained at room temperature. Compared with the lowest carrier concentration ∼2×1018 cm−3 obtained on thin InN films grown at the same condition, the conclusion is that impurities from the growth environment are not responsible for the high background doping of InN. Instead, some structural defects or substrate/buffer impurities may be the major source of the unintentional doping, which can be reduced by growing thicker films.

Some results on Mg and Be doping of InN will be reported as well. To date, all Mg and Be doping attempts have resulted in n-type material.

Defects can be conveniently categorized into three types: point, line, and areal. In GaN, the important point defects are vacancies and interstitials; the line defects are threading dislocations; and the areal defects are stacking faults. We have used electron irradiation to produce point defects, and temperature-dependent Hall-effect (TDH) and deep level transient spectroscopy (DLTS) measurements to study them. The TDH investigation has identified two point defects, an 0.06-eV donor and a deep acceptor, thought to be the N vacancy and interstitial, respectively. The DLTS study has found two point-defect electron traps, at 0.06 eV and 0.9 eV, respectively; the 0.06-eV trap actually has two components, with different capture kinetics. With respect to line defects, the DLTS spectrum in as-grown GaN includes an 0.45-eV electron trap, which has the characteristics of a dislocation, and the TDH measurements show that threading-edge dislocations are acceptor-like in n-type GaN. Finally, in samples grown by the hydride vapor phase technique, TDH measurements indicate a strongly n-type region at the GaN/Al2O3 interface, which may be associated with stacking faults. All of the defects discussed above can have an influence on the dc and/or ac conductivity of GaN.

Defects can be conveniently categorized into three types: point, line, and areal. In GaN, the important point defects are vacancies and interstitials; the line defects are threading dislocations; and the areal defects are stacking faults. We have used electron irradiation to produce point defects, and temperature-dependent Hall-effect (TDH) and deep level transient spectroscopy (DLTS) measurements to study them. The TDH investigation has identified two point defects, an 0.06-eV donor and a deep acceptor, thought to be the N vacancy and interstitial, respectively. The DLTS study has found two point-defect electron traps, at 0.06 eV and 0.9 eV, respectively; the 0.06-eV trap actually has two components, with different capture kinetics. With respect to line defects, the DLTS spectrum in as-grown GaN includes an 0.45-eV electron trap, which has the characteristics of a dislocation, and the TDH measurements show that threading-edge dislocations are acceptor-like in n-type GaN. Finally, in samples grown by the hydride vapor phase technique, TDH measurements indicate a strongly n-type region at the GaN/Al2O3 interface, which may be associated with stacking faults. All of the defects discussed above can have an influence on the dc and/or ac conductivity of GaN.

Defect concentrations in molecular beam epitaxial (MBE) GaAs range from 1012 to 1020 cm-3 as the growth temperature is lowered from 600 to 200 °C; however, very high quality layers can be grown over this whole range. The dominant defect is the As antisite, but there is also good evidence for As interstitials and gallium vacancies. The particular form of the As antisite center in low—temperature (LT) MBE GaAs is not known at this time, but it is definitely not EL2, because both the thermal activation energy and the electron capture cross section differ significantly. However, other features, such as the EPR spectrum and metastable—to—normal recovery kinetics are identical to those of EL2. The donor (As antisite) to acceptor ratio seems to hold at about one order of magnitude as growth temperature is varied from 200 — 400 °C; thus, the Fermi level stays near mid—gap over this whole range. However, hopping conduction among the As antisite centers is strong for samples grown between 200 and 300 °C and keeps the material from being semi—insulating, while for those grown between 350 — 480 °C, the resistivity is greater than 107 Ω cm. The annealing dynamics are particularly interesting and include such features as the mobility going through a sharp maximum at an annealing temperature of 400 °C for a layer grown at 200 °C. The donor and acceptor concentrations can be determined both by Hall effect and absorption measurements as the layer is annealed up to 600 °C. Above 550 °C, large precipitates are formed. The relative roles of the precipitates and point defects in influencing compensation, lifetime, and device characteristics are a source of much controversy and will be discussed.

From electron-irriadiation studies, it is known that point defects can strongly affect the electrical properties of GaAs-based MESFET's, MODFET's, solar cells, resonant-tunneling diodes, MIMIC circuits and other devices. As an example, 1 × 1016 cm−2, 1 MeV electrons reduce the transconductance in a 1 μm by 200 μm MESFET by nearly an order of magnitude. Fortunately, annealing at 350 °C for 10 min. can largely restore the device performance, although not without some adverse effects. Point defects, or simple point defect complexes, can also exist in as-grown GaAs and affect devices in several different ways. For example, an As-rich stoichiometry can lead to an abundance of Ga vacancies, and thus to a higher Si donor activation in implanted MESFET devices; however, it can also promote an increase in unwanted impurities which sit on the Ga site. As another example, extremely high (> 3 × 1019 cm−3 ) concentrations of As arntisites, which are found in MBE GaAs grown at 200°C, lead to very unusual electrical and optical properties, and make possible a highly useful buffer material anid a very fast photoconductive switch. However, there are also adverse effects here, such as slow-transients in some MODFET devices, which may result from defect diffusion. Thus, the effects of point defects in GaAs devices must be understood.