Abstract

In the field-effect transistors based on the wide-band-gap nitride heterostructures, the dielectric layers are in widespread use as one of the main elements in the active regions of the devices and the passivation layers. Stringent requirements are imposed on the dielectrics in terms of the high dielectric capacitance, large band-gap energy, and the coating integrity. Furthermore, the films must withstand high electric fields and have a low surface state density in the dielectric/semiconductor interface. For these purposes, the low temperature films grown by plasma-enhanced chemical vapor deposition, atomic layer deposition (ALD), and plasma-enhanced deposition are usually used as effective coatings. The ALD films of Al₂О₃, SiN_х (Si₃N₄), SiON, and ALD AlN are used most often, and offer the greatest promise for the AlGaN/GaN heterostructures. The influence of the passivation of the ALD Al₂O₃, SiN_x, and SiON coatings of various thicknesses on the change of the charge and the density of the states of the AlGaN/GaN heterostructures is investigated. The physical parameters of the structures are estimated by the C–V characteristics measured on various frequencies and the I–V characteristics. It is demonstrated, according to the examined energy band diagrams of the structures at various control voltages, and estimation of the elemental composition of the films by the method of Auger electron spectroscopy, that the reason for the generation of a high positive charge at the deposition of the ALD Al₂O₃ and SiN_x films is the occurrence of an additional piezoelectric charge in the buffer layer of AlGaN. It is demonstrated that use of the SiON films with the oxygen concentration in them higher than 3% does not result in the generation of an additional positive charge but can initiate current fluctuations during the measurement of the I–V characteristics. A possible mechanism of carrier transport in the space charge region resulting in such fluctuations is discussed.

中文翻译：

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AlGaN / GaN HEMT中作为钝化涂层的Al 2 O 3，SiN x和SiON的ALD膜

摘要

在基于宽带隙氮化物异质结构的场效应晶体管中，介电层被广泛用作器件的有源区和钝化层中的主要元素之一。就高介电电容，大带隙能量和涂层完整性而言，对电介质提出了严格的要求。此外，这些膜必须承受高电场并且在介电/半导体界面中具有低的表面态密度。为此，通常将通过等离子体增强化学气相沉积，原子层沉积（ALD）和等离子体增强沉积而生长的低温膜用作有效涂层。Al的ALD膜₂ О ₃，氮化硅_х（SI ₃N ₄，SiON和ALD AlN最常使用，它们为AlGaN / GaN异质结构提供了最大的希望。研究了各种厚度的ALD Al ₂ O ₃，SiN _x和SiON涂层的钝化对电荷变化和AlGaN / GaN异质结构态密度的影响。结构的物理参数是通过在各种频率和I – V上测得的C – V特性来估计的特征。根据在各种控制电压下检查的结构能带图，以及通过俄歇电子能谱法估算薄膜的元素组成，证明了在沉积过程中产生高正电荷的原因ALD Al ₂ O ₃和SiN _x膜的问题是在AlGaN缓冲层中出现了额外的压电电荷。结果表明，使用其中氧浓度高于3％的SiON膜不会导致产生额外的正电荷，但会在I – V测量期间引发电流波动特征。讨论了导致这种波动的空间电荷区域中载流子传输的可能机制。