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In the case of molecular beam epitaxy (MBE), the Mg acceptors are electrically active in the as‐grown material and a priori no additional annealing procedure is necessary. However, there are still some peculiarities in the electrical properties of ammonia‐process grown GaN:Mg and some annealing effect can be observed. Additionally, the character of weak temperature dependence in the vicinity of room temperature suggests that to describe the conduction process an additional conduction channel not related to the free carriers in the valence band must be taken into account. For these reasons, this article presents the results of low‐temperature resistivity and Hall Effect studies of Mg‐doped, ammonia‐process‐grown GaN. The studied samples are grown on low‐temperature buffers of GaN deposited on a sapphire substrate. High‐temperature annealing process (≈800 K) is carried out for all of them. The temperature dependences of the electrical transport properties before and after the annealing procedure are especially investigated at temperatures ranging from 10 up to 300 K. It is found that the low temperatures transport properties are sensitive to the annealing procedure and to describe the observed effects the hopping phenomena must be taken into account. [ABSTRACT FROM AUTHOR]

Hall effect and capacitance-voltage C(V) measurements were performed on p-type GaN:Mg layers grown on GaN templates by molecular beam epitaxy with a high range of Mg-doping concentrations. The free hole density and the effective dopant concentration NA-ND as a function of magnesium incorporation measured by secondary ion mass spectroscopy clearly reveal both a magnesium doping efficiency up to 90% and a strong dependence of the acceptor ionization energy Ea with the acceptor concentration NA. These experimental observations highlight an isolated acceptor binding energy of 245±25 meV compatible, at high acceptor concentration, with the achievement of p-type GaN:Mg layers with a hole concentration at room temperature close to 1019 cm-3. [ABSTRACT FROM AUTHOR]

High quality single crystalline n-type ZnO films, with a thickness of 200 nm, were grown on top of AlN/GaN layers under 25 W, 50 W and 100 W sputtering powers. The AlN and p-type GaN layers were deposited by metalorganic chemical vapor deposition (MOCVD). From X-ray diffraction measurements, the samples exhibited the (000 l) peaks corresponding to both ZnO, GaN and AlN monocrystalline layers. As the sputtering power was increased, the ZnO grain size increased and the dislocation density decreased. This result is supported by a reduction of the rms values obtained on the ZnO layers from Atomic Force Microscopy (AFM) results. In addition, photoluminescence peaks of ZnO at 372 nm, 375 nm and 380 nm were seen as dependent on the sputtering power. We have used an AlN electron blocking layer between ZnO and GaN films to improve the electroluminescence from the n-ZnO side. Room temperature electroluminescence (EL) of the LEDs demonstrated near UV-blue emission consisting of predominating peaks centred at 405 nm, 390 nm and 380 nm for the device with ZnO deposited at 25 W, 50 W and 100 W sputtering powers, respectively. Moreover, the I-V curves of the LEDs showed a rectifying behavior with 6.8 V, 6.4 V, 5.2 V threshold voltages for 25 W, 50 W and 100 W values. AlN/GaN/AlN/ZnO Tandem LED [Display omitted] • We presented a comprehensive and fine-tuned measurements and calculations of the n-ZnO/AlN/p-GaN/AlN hybrid type LEDs fabricated with 25 W, 50 W and 100 W sputtering powers of ZnO films. We have shown how a strong sputtering power such as 100 W has a curative effect on the crystallization of ZnO, • The intentionally used AlN electron blocking layer sandwiched between GaN and ZnO served as both a better nucleation of GaN and passivation layer, which can lead to a superior current spreading over the entire active area, and this combined with ZnO produced at high sputtering power was performed to further improve the efficiency of LED with higher and stronger light emission intensity than a conventional LED. • In this design, by depositing the AlN nucleation layer, we have also prevented the interphase, which has many insulating roles like GaOx. Thus, a better current transmissio- mechanism has been formed. • We fabricated the ZnO/GaN heterojunction with the AlN EBL layer by utilizing the continuous innovations in device fabrication techniques and analyzed in detail different application parameters such as crystallite sizes, dislocation densities and tensile stress including surface mechanisms all derived with XRD analysis. The Electroluminescence results were examined that light emission shifted from the blue region to near UV when switching from 25 W to 100 W. • The conclusions were supported by the energy band diagram by using the Anderson model, the energy barrier for electrons ΔEC, and holes ΔEV, at the interface of ZnO/AlN and GaN/AlN were obtained. Hall effect and secondary ion mass spectroscopy (SIMS) measurements were taken before and after AlN growth were obtained to explain the effects of possible H- and C- impurities, and our results show a remarkable difference in hole concentration and resistivity values. [ABSTRACT FROM AUTHOR]

Electrical transport (resistivity and Hall Effect) have been studied in silicon doped aluminum nitride (AlN) thick epitaxial layers from 250 K up to 1000 K. The investigated samples, grown by molecular beam epitaxy were characterized by n-type conduction with an ambient temperature free carrier concentration of about ∼ 1 × 10 15 cm −3 . The donor level, situated about 250 meV below the conduction band edge, was found to be responsible for the experimentally observed increase of free carrier concentration with temperature. The temperature dependence of carrier mobility has been analyzed in the framework of a multimode scattering model. In the investigated samples the main scattering mechanism is supposed to be dislocation scattering. [ABSTRACT FROM AUTHOR]