We report the morphological and compositional characteristics and their effect on optical properties of Er-doped GaN grown by solid source molecular beam epitaxy on sapphire and hydride vapor phase epitaxy GaN substrates. The GaN was grown by molecular beam epitaxy on sapphire substrates using solid sources ͑for Ga, Al, and Er͒ and a plasma gas source for N 2 . The emission spectrum of the GaN:Er films consists of two unique narrow green lines at 537 and 558 nm along with typical Er 3ϩ emission in the infrared at 1.5 m. The narrow lines have been identified as Er 3ϩ transitions from the 2 H 11/2 and 4 S 3/2 levels to the 4 I 15/2 ground state. The morphology of the GaN:Er films showed that the growth resulted in either a columnar or more compact structure with no effect on green light emission intensity. © 1999 American Vacuum Society. ͓S0734-211X͑99͒06303-9͔The optical properties of rare earth ͑RE͒ elements ͑such as Nd, Er, Pr͒ have led to many important photonic applications, including solid state lasers, telecommunications ͑opti-cal fiber amplifiers, fiber lasers͒, optical storage devices, displays. In most of these applications the host materials for the REs were various forms of oxide and nonoxide glasses. The emission can occur at visible or infrared ͑IR͒ wavelengths depending on the electronic transitions of the selected RE element and the excitation mechanism. Semiconductors doped with REs such as Pr and Er have exhibited only the lowest excited state as an optically active transition. However, the presence of these transitions at IR wavelengths ͑1.3 and 1.54 m͒ coincident with minima in the optical loss of silica-based glass fibers utilized in telecommunications combined with the prospect of integration with semiconductor device technology has sparked considerable interest.The III-N semiconducting compounds are of particular interest as hosts for REs because of their direct band gap and high level of optical activity even under conditions of rather high defect density, which would quench emission in other smaller-gap III-V and wide-gap II-VI compounds. Examples of other RE-doped wide band gap semiconductors ͑WBGS͒ which have been reported include GaP, 1 SiC, 2 and III-V compounds.3 Advantages of WBGS over other semiconductors and glasses include chemical stability, carrier generation ͑to excite the rare earths͒, and physical stability over a wide temperature range. The doping of III nitrides ͑GaN, AlN͒ with Er by molecular beam epitaxy ͑MBE͒ and metal-organic chemical vapor deposition ͑MOCVD͒ both during growth and postgrowth by ion implantation has been reported. [4][5][6][7][8][9][10][11] The successful in situ incorporation 12-14 of Er into AlN and GaN by MBE and its IR emission characteristics have been reported by other groups. None of these articles in the literature report emission in the visible range from Er-doped III-nitrides. Recently, our group has reported 15-18 the in situ incorporation of Er into GaN by MBE on both sapphire and silicon leading to room temperature visible and IR emission b...
Hydrogen decrepitation as a highly efficient and excellent crushing method is widely used in the preparation of NdFeB magnets [1] . However, this method still exist many difficulties in the industrial preparation for 2:17 type SmCo alloys owing to high hydrogen pressure . Our previous work [2] has reported 2:17 type SmCo alloys occur HD at room temperature and hydrogen pressure of 0 .3 MPa and has shown that Fe atom improved hydrogenation decrepitation ability of alloys by improving hydrogen-absorbing ability of 1:7 phase . But the mechanism that Fe improve hydrogen-absorbing ability of the 1:7 phase still need further study . In addition, subsequent degassing behaviour of alloys have been studied by using DSC . The alloy compositions in this study are Sm(Co bal Fe x Cu 0 .053 Zr 0 .02 ) 7 .84 (x=0 .2,0 .3,0 .4,0 .5) alloy . Fig .1(a) shows that the alloy with x=0 .2 was not decrepitated for extremely low hydrogen absorption while the alloys with x=0 .3,0 .4 and 0 .5 are decrepitated after absorbing more than 0 .15 wt% hydrogen at room temperature and hydrogen pressure of 0 .4 MPa . It can be seen that hydrogenation ability for the alloys is obviously improved with increasing Fe content . DSC curves for dehydrogenation of alloys are showed in Fig .1(b) . It can be seen that x≥0 .3 alloys exhibit endothermic peak except alloy with x=0 .2 . Kwon [3] and Zakotnik [4] both show that dehydrogenation temperature of 2:17 type SmCo alloys is 200 0C . According to XRD showed in Fig .1(c), the main phase in alloys is 1:7 phase and some alloys also consist of 2:7 phase and 1:5 phase . So it seems that the endothermic peaks occurred at about 2000C and 160 0C could be dehydrogenation temperature of 1:7 phase and of 2:7 phase, respectively . XRD results show that the peaks of 1:7 phase for the hydrogenated alloys with x=0 .3, 0 .4 and 0 .5 occur at lower angles which indicate that the unit cells have expanded after absorbing hydrogen without a change in the crystal structure . The same results can also be obtained from the lattice parameters of 1:7 phase for alloys showed in Fig .2 . Firstly, H 2 molecule is absorbed on the surface of alloys, which is called physical adsorption . Then H 2 molecule is broken into H atom when activation energy is offered, which is called chemical adsorption . H atom absorbed on the surface will enter into lattice gap and diffuse toward the inside of alloys . In the end, the hydride is produced in the form of solid solution . It can be seen that a, c and V of 1:7 phase for alloys increase with increasing Fe content because the atomic radius of Fe is larger than that of Co, which indicate H atoms can more easily enter into lattice gap . In addition, electronegativity of Fe atom is 1 .83, lower than that of Co atom(1 .88) . It is known that electronegativity of H atom is 2 .20 . The greater electronegativity difference for two atom, The easier combination between two atom . So the addition of Fe atom lead to decreasing of activation energy and is conductive to chemical adsorption . Thus, the imp...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.