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

高效的负电子亲和势（NEA）器件作为冷发射极，实现高速处理和高性能显示，是当今信息社会的迫切需求。具有宽带隙能量的GaN是一种很有前途的器件材料。然而，目前，GaN器件制造在不导电的蓝宝石衬底上。这是GaN器件开发中最严重的问题。为了解决这一问题，本研究计划开发了在GaP半导体衬底上制备GaN厚层的技术，采用我们开发的"成分转换技术"在晶格失配的衬底上生长出所需成分的合金层。其原理是基于材料的化学键强度的差异。在本研究中，我们尝试了两种可能性：1）在650 ℃至850 ℃的温度范围内，在NH_3气体中处理生长在GaP衬底上的GaAs层，以仅将GaAs层转化为GaN，GaP衬底表面在约1000 ℃的较高温度范围内直接氮化。在前一种情况下，在后一种情况下，在1000 ℃下1小时后可以形成具有3 μ m厚度的GaN层。在GaP衬底上使用这些GaN层，我们尝试用蒸发法在其上生长GaN，得到了超过100 μ m的厚GaN层，从而开发出了可用于GaN生长的半导体GaP衬底上的GaN层。这些成果将在NEA器件和其他GaN器件中取得进展

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