The deep levels in GaN associated with yellow luminescence transitions have been investigated using photoluminescence, Hall measurements, and deep level transient spectroscopy (DLTS). Hall measurements on Si-doped GaN show the presence of donor levels at ∼18, ∼35, and ∼70 meV, which are respectively associated with the Si shallow donors, O impurities, and the nitrogen vacancies (VN). DLTS measurements, on the other hand, reveal trap levels at Ec−0.1 eV, Ec−(0.2–0.24) eV, and Ev+0.87 eV. The trap level at Ec−0.1 eV obtained from DLTS can be correlated to the 70 meV deep donor (VN) obtained from Hall measurements. The deep donor band at Ec−(0.2–0.24) eV is attributed to the ON related defect complex decorated along dislocation sites while the hole level at Ev+0.87 eV is attributed to the Ga vacancy (VGa). Thermal annealing at 750 °C in nitrogen ambient results in reduction of yellow luminescence, which could be due to decrease in the concentration of VN and ON-related defect complexes. From these observations, we propose that yellow luminescence in GaN arises from the transitions from the Ec−(0.2–0.24) eV levels to the deep level at Ev+0.87 eV.

The piezoelectric field generated at the AlyInxGa1−x−yN∕GaN interface creates a two-dimensional electron gas (2DEG). The maximum 2DEG mobility in AlyInxGa1−x−yN∕GaN, for a nominal composition of x=0.01 and y=0.07, is obtained for the 40-nm-thick quaternary epilayer. With further increase in the AlyInxGa1−x−yN thickness, the mobility drops due to the generation of V defects and misfit dislocations. The 2DEG carrier concentration increases with the thickness due to the composition pulling effect observed during growth where the Al content increases toward the surface. This effect coupled with the stronger piezoelectric field results in a significant band bending and a deeper potential well is created for the sample with a thicker AlInGaN epilayer. The integrated intensity ratio of the photoluminiscence emission from the 2DEG and the AlInGaN band-edge emission, I2DEG∕IBE, is studied as a function of temperature for AlInGaN epilayers of different thickness. The effect of strain relaxation and V-pit formation on the 2DEG confinement in AlInGaN∕GaN is also discussed.

Cobalt was deposited on single-crystal Ge(001) surface at ∼350°C by electron-beam evaporation in an ultrahigh-vacuum transmission electron microscope. The deposited Co reacts with Ge to form nanosized islands with the cobalt germanide Co5Ge7 phase. The Co5Ge7 islands show square and rectangular shapes. Two epitaxial orientation relationships between Co5Ge7 and Ge were observed: Co5Ge7 ⟨110⟩(001)‖Ge⟨100⟩(001) and Co5Ge7⟨001⟩(110)‖Ge⟨100⟩(001).

Schottky contacts of Pt germanide films formed on n-Ge(001) through solid-state reaction between Pt and Ge(001) via rapid thermal annealing were investigated. Almost identical effective barrier heights of ∼0.619–0.626eV were obtained for PtGe∕n-Ge(001), Pt2Ge3∕n−Ge(001), and PtGe2∕n-Ge(001) Schottky contacts from current-voltage measurements. From the effective barrier height values, actual barrier heights of ∼0.653–0.663eV were determined by taking into account the image force induced barrier lowering in the presence of strong inversion layers at the interfaces. The actual barrier height values obtained were further validated by the good agreement between experimental and simulation results for capacitance-voltage characterization.

We report a systematic temperature-dependent Raman scattering study of NiSi thin films. In agreement with the basic anharmonic theory, the strong Raman peak from NiSi at about 214 cm −1 shows phonon softening and broadening with an increase in the sample temperature. Comparative study of the temperature dependence of this first-order Raman peak from NiSi powder and the film show that NiSi layers of thickness 15-90 nm are under tensile thermal stress. The results also show that the total phonon shift observed in the temperature range 80-500 K is independent of the silicide film thickness. We have also shown that Raman spectroscopy is a faster and more sensitive technique than x-ray diffraction for phase identification in NiSi nanolayers, hence Raman scattering can be used as a valuable tool for in situ growth and process monitoring of nickel silicides.