Jha Jaya, Ganguly Swaroop, Saha Dipankar
Department of Electrical Engineering, Indian Institute of Technology Bombay, Powai, Mumbai-400076, India.
Nanotechnology. 2021 May 12;32(31). doi: 10.1088/1361-6528/abfb99.
GaN-based high electron mobility transistors (HEMTs) have received much attention due to their potential usage in radio-frequency and high power applications. However, the development of logic gates has remained mostly elusive due to the still challenging reliable operation of the field-effect enhancement-mode n-transistor and nascent stage for the p-transistor. The n-transistor behavior is mainly achieved by combining the aggressive thinning down of the barrier layer, using charged oxides, and p-doping the cap layer. The p-transistor generally requires a heavily doped p-GaN layer. The realization of both transistors on the same substrate remains challenging due to the conflicting requirements for n- and p-transistors. Here, we propose a GaN-based field-effect complementary transistor device using a p-doped InGaN/GaN superlattice (SL) structure on top of the barrier layer of the HEMT heterostructure. The SL structure changes the electrostatics of the heterostructure by the formation of a two-dimensional hole gas region. An undoped SL structure is shown to be enough to lift the conduction band-edge above the Fermi level to convert the n-transistor from depletion-mode (D-mode) to enhancement-mode (E-mode). The lifting of the bands, in turn, creates a natural quantum-well for the holes in the p-transistor. An additional p-doping of the SL moves the threshold voltage of the E-mode n-transistor further into a positive direction and increases the hole density in the quantum-well E-mode p-transistor. The SL structure, which can be grown by a standard epitaxial process, facilitates the realizations of both the n- and p-transistors. The characteristics of individual devices are further analyzed. A digital inverter gate is simulated, and critical static and dynamic performance parameters are reported. The propagation delay indicates that logic operations can be done at a very high speed compared to those offered by other conventional semiconductors.
基于氮化镓的高电子迁移率晶体管（HEMT）因其在射频和高功率应用中的潜在用途而备受关注。然而，由于场效应增强型n晶体管的可靠运行仍具有挑战性，且p晶体管尚处于起步阶段，逻辑门的发展大多仍难以实现。n晶体管的行为主要通过结合对势垒层进行激进的减薄、使用带电氧化物以及对帽层进行p型掺杂来实现。p晶体管通常需要一个重掺杂的p-GaN层。由于n晶体管和p晶体管的要求相互冲突，在同一衬底上实现这两种晶体管仍然具有挑战性。在此，我们提出一种基于氮化镓的场效应互补晶体管器件，该器件在HEMT异质结构的势垒层顶部采用p型掺杂的InGaN/GaN超晶格（SL）结构。该SL结构通过形成二维空穴气区域改变了异质结构的静电特性。结果表明，一个未掺杂的SL结构足以将导带边缘提升至费米能级以上，从而将n晶体管从耗尽模式（D模式）转换为增强模式（E模式）。能带的提升反过来又为p晶体管中的空穴创造了一个自然量子阱。对SL进行额外的p型掺杂会使E模式n晶体管的阈值电压进一步向正向移动，并增加量子阱E模式p晶体管中的空穴密度。这种可以通过标准外延工艺生长的SL结构，有助于实现n晶体管和p晶体管。进一步分析了单个器件的特性。模拟了一个数字反相器门，并报告了关键的静态和动态性能参数。传播延迟表明，与其他传统半导体相比，逻辑操作可以以非常高的速度进行。
