氧化鋁超晶格之發光二極體

Abstract

我們利用超晶格結構提昇入射電子的能量，成功地在矽晶片上作出發光元件。超晶格穿透二極體主要是由氧化鋁以及由錫所參雜之氧化銦交替沉積而形成。發光波長主要在750nm，並且發光的強度是熱載子在金氧半場效電晶體中發光的一千倍，以及傳統穿透二極體的一萬倍。在足夠高的外加電壓下，亦可以以肉眼直接觀察到其較高能的光。我們認為在順偏時，電子經由超晶格中量化而形成的能量帶入射至矽基板，並以發光的形式與價電帶的電洞復合，期間熱電子亦伴隨撞擊游離的現象。而使用氧化鋁除了有較好的介電質特性外，其高介電係數亦可以有效的提昇在矽基板表面的電場。較高的表面電場可以有較多的載子聚集，以及較小的載子分布範圍，因此載子會有較大的額外動量。在動量守恆的前提下，電子與電洞在矽基板內進行發光形式的復合則可以更容易達成。

An ITO/superlattice/p-Si tunnel diode used as a light-emitting device was made on the Si substrate. The superlattice (SL) is formed by alternatively depositing ITO and Al2O3 materials, and the thickness of each SL layer is in the range of 10~20Å. At a forward bias -3V, strong and uniform electroluminescence (EL) from SL tunnel diode is detected, and the emitted light is mainly located in the infrared region. The light intensity from SL tunnel diode is three orders of magnitude larger than hot-carrier induced light emission in MOSFETs, and near 10000 greater than gate-injected MOS tunnel diode. At higher biasing conditions (>-7V), the high-energy tail can even be seen by naked eyes. We thought electrons from the minibands of SL tunnel into Si substrate and relax their extra energy via radiative recombination and/or impact ionization. The SL structure is used to elevate the injecting electron energy and reduce electric field inside Al2O3 layers. The use of Al2O3 arises from the advantages of its good dielectric integrity and high permittivity. Better hole confinement and larger extra momentum of carriers are found in the Al2O3 SL tunnel diodes. The momentum conservation for radiative recombination is easier to achieve, thus EL from the Si substrate will be enhanced.