Formation of GaN layers by liquid phase epitaxy and its application to high efficient NEA devices

在当今信息化社会，人们迫切需要高效的负电子亲和（Negative Electron Affinity，简称NEA）器件作为实现高速处理和高性能显示的冷发射器。具有宽能带能的氮化镓是一种很有前途的器件材料。然而，目前，氮化镓器件是在不导电的蓝宝石衬底上制造的。这是GaN器件开发中最严重的问题。为了克服这一问题，本研究项目开发了在GaP半导体衬底上制备GaN厚层的技术。我们使用了我们自己开发的“成分转换技术”，在晶格不匹配的衬底上生长出具有所需成分的合金层。其原理是根据材料化学键强度的不同而定的。在本研究中，GaAs或GaP通过与NH_3的化学反应转化为具有强键的GaN。在实验中,我们尝试了两种可能性:1)砷化镓衬底层上生长差距治疗NH_3气体的温度范围650゚C - 850 C゚将仅对氮化镓砷化镓层,和2)基板表面的差距直接氮化在更高的温度范围约1000゚C,在前一种情况中,整个5妈妈的砷化镓层厚度可以被改装成甘1小时后850゚C。后一种情况下，在1000℃的温度下，1小时后可以形成3mum厚度的GaN层。利用这些GaN层在GaP衬底上进行了蒸发生长试验，得到了超过100mum的极厚GaN层。因此，可以用于GaN生长的半导体GaP衬底上的GaN层已经开发出来。这些成果将在NEA器件和其他GaN器件上取得进展

High efficient NEA (Negative Electron Affinity) devices are required as a cold emitter realizing high speed processing and/or high performance display, which are eager in recent information-oriented society. GaN with wide bandgap energy is a promising material for the devices. However, at the present, GaN devices are fabricated on a sapphire substrate which is electrical non-conductive. This is the most severe problem in developing GaN devices. To overcome this problem, this research project has been made to develop the preparation technique of a GaN thick layer on a GaP semiconductor substrate.We used the "Compositional conversion technique" which was developed by us to grow an alloy layer with desired composition on a lattice mismatched substrate. The principle is based on the difference in chemical bond strength of the materials. In this research, GaAs or GaP is converted to GaN with strong bonds through chemical reaction with NH_3.In the experiments, we tried two possibilities : 1) GaAs layers grown on a GaP substrate were treated in NH_3 gas at the temperature range of 650ﾟC to 850ﾟC to convert only the GaAs layer to GaN, and 2) the surface of GaP substrates was directly nitrided at higher temperature range of about 1000ﾟC, In the former case, whole of the GaAs layer with 5mum thickness could be converted to GaN after 1 hour at 850ﾟC.In the later case, GaN layers with 3mum thickness could be formed after 1 hour at 1000ﾟC.Using these GaN layers on GaP substrates, we tried the growth of GaN on it by evaporation method, and very thick GaN layers, exceeded 100mum, could be obtained.Thus, the GaN layers on a semiconductor GaP substrate available to GaN growth has been developed. These fruits should make progress in NEA devices and other GaN