Vapor phase growth system and its use in the preparation of several III-V compound semiconductors

Vapor phase growth and properties of semiconductor material

Optical Properties of III-Mn-V Ferromagnetic Semiconductors

We review the first decade of extensive optical studies of ferromagnetic, III-Mn-V diluted magnetic semiconductors. Mn introduces holes and local moments to the III-V host, which can result in carrier mediated ferromagnetism in these disordered semiconductors. Spectroscopic experiments provide direct access to the strength and nature of the exchange between holes and local moments; the degree of itineracy of the carriers; and the evolution of the states at the Fermi energy with doping. Taken together, diversity of optical methods reveal that Mn is an unconventional dopant, in that the metal to insulator transition is governed by the strength of the hybridization between Mn and its p-nictogen neighbor. The interplay between the optical, electronic and magnetic properties of III-Mn-V magnetic semiconductors is of fundamental interest and may enable future spin-optoelectronic devices.Comment: Topical Revie

Paramagnetic GaN:Fe and ferromagnetic (Ga,Fe)N - relation between structural, electronic, and magnetic properties

We report on the metalorganic chemical vapor deposition (MOCVD) of GaN:Fe and (Ga,Fe)N layers on c-sapphire substrates and their thorough characterization via high-resolution x-ray diffraction (HRXRD), transmission electron microscopy (TEM), spatially-resolved energy dispersive X-ray spectroscopy (EDS), secondary-ion mass spectroscopy (SIMS), photoluminescence (PL), Hall-effect, electron-paramagnetic resonance (EPR), and magnetometry employing a superconducting quantum interference device (SQUID). A combination of TEM and EDS reveals the presence of coherent nanocrystals presumably FexN with the composition and lattice parameter imposed by the host. From both TEM and SIMS studies, it is stated that the density of nanocrystals and, thus the Fe concentration increases towards the surface. In layers with iron content x<0.4% the presence of ferromagnetic signatures, such as magnetization hysteresis and spontaneous magnetization, have been detected. We link the presence of ferromagnetic signatures to the formation of Fe-rich nanocrystals, as evidenced by TEM and EDS studies. This interpretation is supported by magnetization measurements after cooling in- and without an external magnetic field, pointing to superparamagnetic properties of the system. It is argued that the high temperature ferromagnetic response due to spinodal decomposition into regions with small and large concentration of the magnetic component is a generic property of diluted magnetic semiconductors and diluted magnetic oxides showing high apparent Curie temperature.Comment: 21 pages, 30 figures, submitted to Phys. Rev.

Investigation of wide bandgap semiconductors for room temperature spintronic, and photovoltaic applications

Suitability of wide bandgap semiconductors for room temperature (RT) spintronic, and photovoltaic applications is investigated. Spin properties of metal-organic chemical vapor deposition (MOCVD) – grown gadolinium-doped gallium nitride (GaGdN) are studied and underlying mechanism is identified. GaGdN exhibits Anomalous Hall Effect at room temperature if it contains oxygen or carbon atoms but shows Ordinary Hall Effect in their absence. The mechanism for spin and ferromagnetism in GaGdN is a combination of intrinsic, metallic conduction, and carrier-hopping mechanisms, and is activated by oxygen or carbon centers at interstitial or similar sites. A carrier-related mechanism in MOCVD-grown GaGdN at room temperature makes it a suitable candidate for spintronic applications. Zinc oxide (ZnO) doped with transition metals such as nickel and manganese and grown by MOCVD is investigated, and bandgap tunability is studied. A bandgap reduction with transition metal doping is seen in ZnO with dilute doping of nickel or manganese. Transition metals could introduce energy states in ZnO that result in a bandgap reduction and could be tuned and controlled by growth conditions and post-growth processing such as annealing, for spintronic and photovoltaic applications”--Abstract, page iii

Surface characterization and luminescence properties of AlN doped with RE elements (Sm, Ho, Gd, Tm)

Rare‐ earth (RE)‐doped III‐nitride broad band‐gap semiconductors have attracted enormous interest as a foundation for optoelectronics devices, which combine the unique luminescence feature of Rare‐earth ions with the electronic properties of the semiconductors. Recent progress toward nitride‐based light emitting diode and light emitting due to electric current devices have been made using crystalline and amorphous AlN and GaN doped with a different lanthanide elements. The Rare‐earth ions’ electronic structures are differ from the other elements and are unique due to an incompletely filled 4Fn shell. The 4F‐orbital electrons lay inside the ion and are protected from the surroundings by the filled 5S2 and 5P6 electron orbitals. When these rare‐earths doped are excited by any external means, intense sharp‐line emission is observed due to intra‐4Fn shells transitions of the rare‐earth ion core. In the present work, sputtered deposited thin films of AlN doped with rare‐earth elements (Sm, Ho, Gd, Tm) are investigated for their structures, luminescence and spectroscopic properties. Thin films were deposited at various temperatures. X‐ray diffraction (XRD) analysis was performed for structural analysis and crystallite size calculation in crystalline films. Scanning electron microscopy was also used to confirm the information obtained from XRD. Luminescence and spectroscopic analysis were performed using photoluminescence tool and Fourier transform infra‐red. The effect of the temperature on the surface morphology and luminescence properties was also studied. Energy dispersive x‐ray analysis was performed on the films to find the constituents and impurities in the samples. Atomic force microscopy was also used for determination of surface roughening, and thermal gravimetric analysis was used to investigate loss of mass of the samples over a range of temperature. This work provides investigations of these materials for their use in photonic and microelectronic devices