Total-Ionizing Dose Mechanisms in Antimony based CMOS Transistors with High-k Dielectric

In this paper we present the effect of ionizing radiation on n and p-channel Antimonide based (Sb) based Quantum Well-Metal-Oxide-Semiconductor-Field-Effect Transistor (QW-MOSFETs). QW-MOSFET's were fabricated on n-channel InAsSb QW and p-channel InGaSb QW and then exposed to ionizing radiation. The n-channel InAsSb QW shows higher radiation sensitivity than the pchannel InGaSb QW due to enhanced hole trapping occurring at the AlInSb barrier/InAsSb QW interface. The transient response of the InAsSb QW MOS structure to radiation induced electron-hole pair generation was evaluated using TCAD simulation. Introduction There is tremendous interest in Antimonide based (Sb) compound semiconductors due to their superior electron and hole transport properties. InGaSb and InAsSb quantum wells (QWs) (Fig.1) are of particular interest as InGaSb offers hole mobilities over 10X than that seen in Si, while n-channel InAsSb QWs offer electron mobilities over 60X over Si (Fig.2). Further, InAsSb and InGaSb QWs share a common Al0.8Ga0.2Sb buffer (Fig.1), facilitating the integration of both p and n-channel devices on a common III-V platform. These strengths make Sb-based devices applicable for use in low power high-speed digital and millimeter wave applications. Sb device technology needs to be resilient to ionizing radiation. To date, the study of the impact of ionizing radiation on III-V devices has been limited to GaAs metal semiconductor field effect transistors (MESFET's), InGaAs/ InAlAs HEMTs, and InAs/AlSb HEMTs [1-2] In this work, we study and analyze the effect of ionizing radiation on Sb-channel nand p-channel QW MOSFETs. Antimony Based Transistors The InAsSb n-channel and InGaSb p-channel QWMOSFETs used in this work were grown on separate substrates. The InAsSb n-channel hetrostructure was grown on a GaAs substrate with a metamorphic Al0.8Ga0.2Sb buffer (Fig 3). The QW is undoped while the Al0.8In0.2Sb barrier layer has been delta-doped with Te to provide carriers to the access regions. A hybrid GaSb/InAlSb barrier layer is utilized. Sb-based materials are especially reactive in atmosphere resulting in a poor high-κ Figure 1. InAlSb and InGaSb QW heterostructures on AlGaSb common metamorphic buffer dielectric/antimonide interface. Adding a thin layer of GaSb to the barrier has been shown to improve passivation of the semiconductor/dielectric interface. The InAsSb QWMOSEFTs were fabricated using a gate-last process with a Al2O3/HfO2/high-κ gate dielectric deposited via Atomic Layer Deposition (ALD) [3-4]. Figure 2. (a) Hole mobility versus hole sheet density at T=300K for Si, and GaInSb QW (b) Electron mobility versus electron sheet density at T=300K for Si, and InAsSb, measured using Hall transport measurements. [3,5] The InGaSb p-channel heterostructure was grown on a GaAs substrate using the same metamorphic Al0.8Ga0.2Sb buffer as the n-channel device (Fig 3). A GaSb/AlInSb hybrid barrier is utilized to confine the InGaSb channel. A thin layer of GaSb is again used to improve the dielectric/semiconductor interface. The p-channel InGaSb QW MOSFETs were fabricated using a self-aligned gatefirst process [5,6] with ALD Al2O3/high-κ gate dielectric. The high quantization in the resulting AlInSb/GaSb/Al2O3 QW lowers lowering the available charge near the interface, thereby reducing the detrimental effect of interface states on hole mobility. [7] Figure 3. (a) InAlSb and (b) InGaSb QW heterostructures Figure 4. (a) ID-VG characteristics for LG=5um InAsSb QWMOSFET at T=300K [3] (b) ID-VG characteristics for LG=5um InGaSb QW-MOSFET at T=300K [5] The ID-VG response for long channel (LG=5.0 um) InAsSb n-channel and InGaSb p-channel QW-MOSFETs are shown in Fig.4 Effective mobilites were extracted from both structures using the split-CV method [3,5] (Fig.6). The InAsSb n-channel device has a peak effective electron mobility over 5,970 cm/V-s, while the InGaSb p-channel shows peak hole mobility of over 900 cm/V-s. RF characterization of short channel InAsSb QW-MOSFET's show a cutoff frequency of 120 GHz and an effective source injection velocity 4X higher than Si NMOS and 1.5X higher than InGaSb NMOS. Figure 5. Extracted effective mobility for InAsSb and InGaSb QW's as a function of carrier density [3-5] Total Ionizing Dose Total Ionizing Dose (TID) experiments were performed on the InAsSb and InGaSb QWMOSFET's. These devices were subjected to X-ray radiation from a 10 keV, source with a dose rate 31.5 krad SiO2/min As shown in Figs 6-8 the InAsSb when exposed to ionizing radiation at high vertical electric field (VG=1.0V) showed significant negative threshold voltage VT shift. At lower vertical electric field (VG=0.2V) the threshold voltage shift was less. Twenty-four hours after radiation exposure the device threshold voltage completely recovered. For InAsSb QWMOSFET, the sub-threshold slope (SS) and transconductance remained relatively unchanged with dose at low vertical electric field, while this was not the case at high vertical electric field (Fig. 9). The negative VT shifts are indicative of induced positively charged hole trapping due to ionizing radiation. Figure 6. Radiation induced VT shift in InAsSb n-channel QW-MOSFET ID-VG characteristics Figure 7. Radiation induced VT shift in InGaSb p-channel QW-MOSFET ID-VG characteristics Figure 8. Radiation induced VT shift as a function of dose for n-channel InAsSb and p-channel InGaSb QWMOSFETs The InGaSb p-channel devices showed sensitivity to ionizing radiation. As shown in Figs. 8-9 there was a negative threshold voltage shift at high vertical electric field (VG=-1V). For the p-channel InGaSb there is a slight degradation in SS and transconductance with increasing radiation dose (Fig.10). However, as shown in Fig. 8, the VT shifts associated with increasing ionizing radiation dose are much less for the p-channel InGaSb device compared to the n-channel InAsSb device. Figure 9. Sub-threshold swing (SS) and transconductance as a function of radiation dose for n-channel InAsSb QWMOSFET Figure 10. Sub-threshold swing (SS) and transconductance as a function of radiation dose for p-channel InGaSb QW-