GaN HEMT器件和GaAs PHEMT器件对比特性研究

发布时间：2018-09-06 12:07

【摘要】：近几十年以来,人类社会经历了三次半导体材料带动的产业革命。第一代Si、Ge材料、第二代GaAs材料和InP以及第三代宽禁带GaN和SiC材料分别引领了微电子领域的发展浪潮,实现了技术上的三次飞跃。GaN以其较高的禁带宽度、高击穿电场等优势,使GaN高电子迁移率晶体管(HEMT)作为第三代半导体器件的优秀代表,在高频微波、大功率、抗高压等方面被广泛应用,在国防、通信、照明、电力、航空航天等领域具有不可替代的地位。GaN材料是一种宽禁带半导体材料,它具有与众不同的自发极化和压电极化效应,使得基于GaN的HEMT器件可以在非掺杂的情况下产生二维电子气。这在HEMT器件中是一巨大的优势。但是这两种极化效应也会在器件沟道内产生—种独有的散射,称为极化库仑场散射(pCF散射)。PCF散射源于GaN HEMT器件源漏间AlGaN势垒层应变分布的不均一性,这种非均匀性使得沿AlGaN/GaN异质界面的极化电荷分布不均,从而产生PCF散射。已有的PCF散射研究仅局限于GaN HEMT器件本身,而没有深入地与其它材料体系的器件进行对比分析研究。本文的GaN HEMT器件与GaAs PHEMT器件对比研究则填补了这一空白。GaAs材料与GaN材料一样,均为直接带隙半导体。它具有一些独特的优点。GaAs赝配高电子迁移率晶体管(PHEMT)不存在GaN HEMT器件固有的自发极化和压电极化效应,其二维电子气来源于势垒层的掺杂。两者都通过栅极来调控沟道载流子的输运,因此GaAs PHEMT是首选的对比器件。通过对比分析研究,可进一步明确PCF散射在GaN HEMT器件中的独特作用,为进一步提升GaN HEMT器件特性奠定基础。本文分别制备了源漏间距为20μm和100μm的不同栅长的GaN HEMT和GaAs PHEMT的中央栅型器件,并对其进行了对比研究。1.GaN HEMT器件和GaAs PHEMT器件的载流子迁移率对比研究。分别测试了 GaN HEMT器件和GaAs PHEMT器件的电容-电压(C-V)特性、电流-电压(Ⅰ-Ⅴ)输出特性、二极管特性和栅源寄生串联电阻(Rs)特性。通过对比分析GaN HEMT器件和GaAs PHEMT器件载流子迁移率发现:在GaN HEMT器件中,载流子迁移率随栅偏压(Vg)变化趋势明显与栅长和源漏间距相关。随着栅长与源漏间距之比Lg/Lsd的减小,PCF散射比重上升,当PCF散射起主导作用时,载流子迁移率随栅偏压增大呈现不断上升的趋势。相同Lg/Lsd比例下,随着栅长Lg的减小,PCF散射增强。在更短的栅长沟道内,AlGaN势垒层应变分布非均匀性增强,PCF散射的作用更强。在GaAs PHEMT器件中,载流子迁移率随栅偏压变化趋势与栅长和源漏间距无关。不同栅长GaAs PHEMT器件的载流子迁移率变化趋势均显著地表现为随栅偏压先上升后下降,并且此趋势不随栅长以及Lg/Lsd的变化而改变。在栅偏压较小时,电离杂质散射起主导作用。随着二维电子气(2DEG)面密度的增加,2DEG对电离杂质散射的库仑屏蔽作用增强,载流子迁移率随着Vg的增加而提高,达到极值点后(此时第二子能带开始填充),随Vg继续增大,2DEG电子密度增加,电离杂质散射继续减弱,极化光学声子散射(POP散射)和界面缺陷散射增强并成为主导散射机制,载流子迁移率随Vg的增加而下降。GaN HEMT器件与GaAs PHEMT器件载流子迁移率随Vg变化曲线差异主要源于GaN HEMT器件独有的PCF散射。2.GaN HEMT器件和GaAs PHEMT器件的栅源寄生串联电阻Rs特性对比研究。Rs特性直接决定了器件跨导。根据栅探针(Gate Probe)方法测试两者随栅偏压变化的Rs特性,对Rs随栅偏压变化特性进行了分析。分析表明,GaN HEMT器件的Rs随栅电流的增大而增强,GaAs PHEMT器件的Rs随栅电流的增加而减弱;对应相同器件结构的GaN HEMT和GaAs PHEMT,GaN HEMT器件Rs的变化率远大于GaAs PHEMT器件Rs的变化率。两者的区别在于:对GaN HEMT器件而言,PCF散射是导致不同栅电流下Rs变化的主要原因;而对于GaAs PHEMT器件而言,Rs变化与电离施主杂质库仑散射有关。GaN HEMT器件没有掺杂,不存在杂质库仑散射,其Rs变化原因只能来源于PCF散射。3.GaN HEMT器件和GaAs PHEMT器件的跨导特性对比研究。通过测定两者的转移特性曲线,微分求导得到相应的跨导特性。发现两者的跨导特性均表现为随栅偏压的增加而先升高后下降。在跨导降低区间,GaAs PHEMT器件的跨导负增长率比GaN HEMT器件的更高。在这里POP散射的增强使得Rs增大引起了跨导的下降,而GaN HEMT器件的PCF散射的影响减缓了跨导的下降幅度。利用PCF散射可减缓跨导衰减的特性,有助于解决GaN器件在功率放大器应用中的线性失真问题。
[Abstract]:In recent decades, human society has experienced three industrial revolutions driven by semiconductor materials. The first generation Si, Ge, second generation GaAs, InP and third generation wide band gap GaN and SiC materials have led the development of microelectronics and achieved three technological leaps. GaN has higher band gap width, high breakdown electric field and so on. GaN high electron mobility transistor (HEMT) is an outstanding representative of the third generation semiconductor devices. It is widely used in high frequency microwave, high power, anti-high voltage and other fields. It has an irreplaceable position in defense, communications, lighting, power, aerospace and other fields. Spontaneous polarization and piezoelectric polarization make it possible for GaN-based HEMT devices to produce two-dimensional electron gases without doping. This is a huge advantage in HEMT devices. But these two polarization effects also produce a unique kind of scattering in the device channel, called polarized Coulomb field scattering (pCF scattering). PCF scattering originates from GaN HEMT devices. The inhomogeneity of the strain distribution in the AlGaN barrier layer between the source and the drain makes the polarized charge distribution along the AlGaN/GaN heterogeneous interface uneven, which results in PCF scattering.The existing research on PCF scattering is limited to GaN HEMT device itself, and has not been deeply compared with other materials. GaAs materials, like GaN materials, are direct band gap semiconductors. GaAs pseudo-high electron mobility transistors (PHEMT) have some unique advantages. GaAs pseudo-high electron mobility transistors (PHEMT) do not have inherent spontaneous polarization and piezoelectric polarization effects of GaN HEMT devices. Their two-dimensional electron gas originates from potential barrier layers. GaAs PHEMT is the preferred contrast device because both of them control channel carrier transport through a gate. The unique role of PCF scattering in GaN HEMT devices can be further clarified by comparative analysis, which lays a foundation for further improving the characteristics of GaN HEMT devices. The source-drain spacing of GaAs PHEMT is 20 and 100 microns respectively. Carrier mobility of GaN HEMT and GaAs PHEMT devices with the same gate length are compared. Capacitance-voltage (C-V) characteristics, current-voltage (I-V) output characteristics, diode characteristics and gate-source parasitic characteristics of GaN HEMT devices and GaAs PHEMT devices are tested respectively. Carrier mobility of GaN HEMT devices and GaAs PHEMT devices are compared and analyzed. It is found that the variation of carrier mobility with gate bias (Vg) is obviously related to gate length and source-drain spacing in GaN HEMT devices. In the same Lg/Lsd ratio, the scattering of PCF increases with the decrease of the gate length Lg. In the shorter channel, the heterogeneity of the strain distribution in the barrier layer of AlGaN increases, and the scattering of PCF becomes stronger. In GaAs PHEMT devices, the variation of the carrier mobility with the gate bias voltage tends to be the same. The carrier mobility of GaAs PHEMT devices with different gate lengths increases first and then decreases with the gate bias, and this trend does not change with the gate length and Lg/Lsd. Ionizing impurity scattering plays a dominant role when the gate bias is small. With the increase of 2-D electron gas (2DEG) surface density, the carrier mobility of GaAs PHEMT devices with different gate lengths increases first and then decreases. Additionally, the Coulomb shielding effect of 2DEG on the scattering of ionized impurities is enhanced, and the carrier mobility increases with the increase of Vg. After reaching the extreme point (at this time the second band begins to fill), with the increase of Vg, the electron density of 2DEG increases, the scattering of ionized impurities continues to weaken, the polarized optical phonon scattering (POP scattering) and the interface defect scattering increase and become. The difference between GaN HEMT device and GaAs PHEMT device in carrier mobility versus Vg is mainly due to the unique PCF scattering of GaN HEMT device. 2. Comparison of Rs characteristics between GaN HEMT device and GaAs PHEMT device. According to Gate Probe method, the Rs characteristics of GaN HEMT devices with gate bias are analyzed. The results show that Rs of GaAs PHEMT devices increase with gate current, Rs of GaAs PHEMT devices decrease with gate current, and Rs of GaN HEMT and GaAs PHEMT, GaN HEMT devices with the same device structure are analyzed. The difference between the two is that PCF scattering is the main reason for Rs variation under different gate currents for GaAs PHEMT devices, while for GaAs PHEMT devices, Rs variation is related to ionizing donor impurity Coulomb scattering. It is found that the transconductance of GaAs PHEMT and GaN HEMT increases first and then decreases with the increase of gate bias. The negative transconductance growth rate of GaN-HEMT devices is higher than that of GaN-HEMT devices. In this case, the increase of POP scattering causes the increase of Rs and the decrease of transconductance. The PCF scattering of GaN-HEMT devices reduces the decrease of transconductance. Problem.
【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN386

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