Visible light emission has been obtained at room temperature by photoluminescence ͑PL͒ and electroluminescence ͑EL͒ from Eu-doped GaN thin films. The GaN was grown by molecular beam epitaxy on Si substrates using solid sources ͑for Ga and Eu͒ and a plasma source for N 2. X-ray diffraction shows the GaN:Eu to be a wurtzitic single crystal film. Above GaN band gap photoexcitation with a He-Cd laser at 325 nm resulted in strong red emission. Observed Eu 3ϩ PL transitions consist of a dominant narrow red line at 621 nm and several weaker emission lines were found within the green through red ͑543 to 663 nm͒ range. Below band gap PL by Ar laser pumping at 488 nm also resulted in red emission, but with an order of magnitude lower intensity. EL was obtained through use of transparent indium-tin-oxide contacts to the GaN:Eu film. Intense red emission is observed in EL operation, with a spectrum similar to that seen in PL. The dominant red line observed in PL and EL has been identified as the Eu 3ϩ 4 f shell transition from the 5 D 0 to the 7 F 2 state.

Growth and morphology of Er-doped GaN on sapphire and hydride vapor phase epitaxy substrates

Blue emission has been obtained at room temperature from Tm-doped GaN electroluminescent devices. The GaN was grown by molecular beam epitaxy on Si(111) substrates using solid sources (for Ga and Tm) and a plasma source for N2. Indium–tin–oxide was deposited on the GaN layer and patterned to provide both the bias (small area) and ground (large area) transparent electrodes. Strong blue light emission under the bias electrode was observable with the naked eye at room temperature. The visible emission spectrum consists of a main contribution in the blue region at 477 nm corresponding to the Tm transition from the G41 to the H63 ground state. A strong near-infrared peak was also observed at 802 nm. The relative blue emission efficiency was found to increase linearly with bias voltage and current beyond certain turn-on levels.

Soaps of the type CFa(CH2),COONa have been prepared with n = 8, 10, and 11. In aqueous solution each soap produces a single, concentration-dependent fluorine magnetic resonance signal. The data readily yield values of the critical micelle concentrations and of the chemical shifts of both the monomeric soap ions and the micellar material. As judged by the cmc values these soaps are essentially similar in their behavior to the ordinary alkyl carboxylates. Comparison of the micelle shifts with shifts observed for the soaps and for CF3(CH2)sCF3 in various solvents shows that the medium surrounding the CFa group when it is in the micelle has characteristics about midway between those of water and of hydrocarbon. This suggests that there is considerable penetration of water into the interior of the micelles, a conclusion also supported by determinations of the fluorine chemical shift of solubilized benzotrifluoride. The micelle shift is virtually unaffected by changes in the size of the micelles brought about either by changing the chain length of the soap or by adding simple electrolytes.( I ) Preliminary results of this work were presented at the 151st (19641, have reported small concentration-dependent changes in the position of the water nmr signal in some detergent solutions.

Visible light electroluminescence (EL) has been obtained from Er-doped GaN Schottky barrier diodes. The GaN was grown by molecular beam epitaxy on Si substrates using solid sources (for Ga, and Er) and a plasma source for N2. Al was utilized for both the Schottky (small-area) and ground (large-area) electrodes. Strong green light emission was observed under reverse bias, with weaker emission present under forward bias. The emission spectrum consists of two narrow green lines at 537 and 558 nm and minor peaks at 413 and at 666/672 nm. The green emission lines have been identified as Er transitions from the H11/22 and S3/24 levels to the I15/24 ground state and the blue and red peaks as the H9/22 and F9/24 Er transitions to the same ground state. The reverse bias EL intensity was found to increase linearly with bias current.

We demonstrated that Sc2O3 thin films deposited by plasma-assisted molecular-beam epitaxy can be used simultaneously as a gate oxide and as a surface passivation layer on AlGaN/GaN high electron mobility transistors (HEMTs). The maximum drain source current, IDS, reaches a value of over 0.8 A/mm and is ∼40% higher on Sc2O3/AlGaN/GaN transistors relative to conventional HEMTs fabricated on the same wafer. The metal–oxide–semiconductor HEMTs (MOS–HEMTs) threshold voltage is in good agreement with the theoretical value, indicating that Sc2O3 retains a low surface state density on the AlGaN/GaN structures and effectively eliminates the collapse in drain current seen in unpassivated devices. The MOS-HEMTs can be modulated to +6 V of gate voltage. In particular, Sc2O3 is a very promising candidate as a gate dielectric and surface passivant because it is more stable on GaN than is MgO.

Visible light emission has been obtained at room temperature by photoluminescence (PL) and electroluminescence (EL) from Pr-doped GaN thin films grown on Si(111). The GaN was grown by molecular beam epitaxy using solid sources (for Ga and Pr) and a plasma gas source for N2. Photoexcitation with a He–Cd laser results in strong red emission at 648 and 650 nm, corresponding to the transition between P03 and F23 states in Pr3+. The full width at half maximum (FWHM) of the PL lines is ∼1.2 nm, which corresponds to ∼3.6 meV. Emission is also measured at near-infrared wavelengths, corresponding to lower energy transitions. Ar laser pumping at 488 nm also resulted in red emission, but with much lower intensity. Indium-tin-oxide Schottky contacts were used to demonstrate visible red EL from the GaN:Pr. The FWHM of the EL emission line is ∼7 nm.

Visible and infrared rare-earth-activated electroluminescence (EL) has been obtained from Schottky barrier diodes consisting of indium tin oxide (ITO) contacts on an Er-doped GaN layer grown on Si. The GaN was grown by molecular beam epitaxy on Si substrates using solid sources for Ga, Mg, and Er and a plasma source for N2. RF-sputtered ITO was used for both diode electrodes. The EL spectrum shows two peaks at 537 and 558 nm along with several peaks clustered around 1550 nm. These emission lines correspond to atomic Er transitions to the I15/24 ground level and have narrow linewidths. The optical power varies linearly with reverse bias current. The external quantum and power efficiencies of GaN:Er visible light-emitting diodes have been measured, with values of 0.026% and 0.001%, respectively. Significantly higher performance is expected from improvements in the growth process, device design, and packaging.