Visible Light Emission from Erbium Doped Yttria Stabilized Zirconia
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VISIBLE LIGHT EMISSION FROM ERBIUM DOPED YTTRIA STABILIZED ZIRCONIA Michael Cross and Walter Varhue Materials Science Program, Dept of Electrical and Computer Eng University of Vermont, Burlington VT 05405, U.S.A ABSTRACT One of the major shortcomings of silicon (Si) as a semiconductor material is its inability to yield efficient light emission. There has been a continued interest in adding rare earth ion impurities such as erbium (Er) to the Si lattice to act as light emitting centers. The low band gap of Si however has complicated this practice by quenching and absorbing this possible emission. Increasing the band gap of the host has been successfully tried in the case of gallium nitride (GaN) [1] and Si-rich oxide (SRO) [2] alloys. A similar approach has been tried here, where Er oxide (ErOx) nanocrystals have been formed in a yttria stabilized zirconia (YSZ) host deposited on a Si (100) substrate. The YSZ is deposited as a heteroepitaxial, insulating layer on the Si substrate by a reactive sputtering technique. The Er is also incorporated by a sputtering process from a metallic target and its placement in the YSZ host can be easily controlled. The device structure formed is a simple metal contact/insulator/phosphor sandwich. The device has been found to emit visible green light at low bias voltages. The advantage of this material is that it is much more structured than SiO2 which can theoretically lead to higher emission intensity. INTRODUCTION Numerous methods have been developed to create an Er doped LED, however, none these have utilized YSZ. Successful light emitting devices have been created in poly-Si [3], SRO [2-5], Si nanocrystals (SNC) [6,7], SiO2 [8], Si nitride (SiN) [9], and most recently in GaN [1,10]. All of these systems have similar basic characteristics. The primary goal is to produce a device which is compatible with current silicon processing techniques in order to be integrated into business as usual (BAU) fabrication. Secondly, the material must have a wide band gap so as not to attenuate the emitted radiation through band to band absorption. In addition, the light emitting material must have very low defect levels. Defects lead to non-radiative recombination and reduce or eliminate emission. Finally, the device must be able to operate efficiently at room temperature. Yttria stabilized zirconia has been considered as a possible replacement for SiO2 as the gate oxide in MOS devices. Published results suggest ease of integration with current Si manufacturing techniques. Having a single crystal structure, YSZ can support the electron acceleration required for impact excitation. High quality crystalline Er doped YSZ films suggest that recombination defects will also be minimized. In order for the device to emit light, the Er must form ErOx complexes. This process is carried out during the anneal step. Multiple annealing conditions were investigated in order to optimize the device performance. Annealing has two main benefits: it repairs
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defects in the bulk film and promotes th
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