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有关结果表明,在氨分子束外延STE3N2系统中,以极高的温度(1 100-1 150℃)让氮化铝缓冲层进行增长是为DHFET(双异质结构场效应晶体管)通道获得高品质GaN(氮化镓)层的关键步骤。缓冲层从包含AlN(氮化铝)、AlGaN/AlN(氮化铝镓/氮化铝)超晶格与AlGaN(氮化铝镓)过渡层的c-蓝宝石衬底开始排列。透射电子显微镜的研究表明,穿透位错密度从AlN层的(2～4)×1010cm-2逐渐减少到顶部GaN活动层的(9～10)×108cm-2。结构质量的改善使得电子迁移率大幅度增长至600～650 cm2/V.s,而在一个1.5μm厚、略含硅元素的GaN顶层中高达3×1016～5×1016cm-3。这些结果表明生长于蓝宝石上的金属有机气相沉积GaN具有良好品质,并且比传统的分子束外延好几倍。在带有AlxGa1-xN顶部阻挡层(x=0.25-0.4)的双异质结构(DH)中使用这样一个GaN层可以让二维电子气中的电子面密度、迁移率与薄层电阻分别在1 300～1 700 cm2/V.s、(1.0～1.8)×1013cm-2与230～400Ω/sq的范围内发生变化。该技术的应用以及为了在SiC(碳化硅)基板上生长而采用的DH设计使得我们可以为0.03～4.0 GHz的超宽频功率放大器(输出功率为2.5 W、增益为17～25 dB、效率为30%)制造出一个带有0.5μm门信号宽度的DHFET。
The results show that the growth of the aluminum nitride buffer layer at very high temperatures (1,100-1,150 ° C) in the ammonia molecular beam epitaxy STE3N2 system provides high quality for the DHFET (double heterostructure field effect transistor) channel GaN (gallium nitride) layer of the key steps. The buffer layer is arranged starting from a c-sapphire substrate comprising AlN (aluminum nitride), AlGaN / AlN (aluminum gallium nitride / aluminum nitride) superlattices and AlGaN (aluminum gallium nitride) transition layers. Transmission electron microscopy studies have shown that the threading dislocation density decreases from (2 ~ 4) × 1010 cm-2 in the AlN layer to (9 ~ 10) × 108 cm-2 in the top GaN active layer. The improvement in the quality of the structure has resulted in a substantial increase of the electron mobility to 600-650 cm2 / V.s, up to 3x1016-5x1016 cm-3 in a 1.5 m thick, slightly Si-containing GaN top layer. These results indicate that the metal-organic vapor grown GaN grown on sapphire has good quality and is several times better than conventional molecular beam epitaxy. The use of such a GaN layer in a double heterostructure (DH) with an AlxGa1-xN top barrier (x = 0.25-0.4) allows electron density, mobility and sheet resistance in two-dimensional electron gas to be in the range of 1 300 to 1 700 cm2 / Vs, (1.0 to 1.8) × 1013 cm-2, and 230 to 400 Ω / sq. The application of this technology and the DH design used to grow on SiC (silicon carbide) substrates allow us to make ultra-wideband power amplifiers of 0.03 to 4.0 GHz with output powers of 2.5 W, gains of 17-25 dB and efficiencies of 30 %) A DHFET with a gate width of 0.5 μm was fabricated.