Influence of SiC hetero-polytype barriers on the performance of IMPATT terahertz diodes

Highlights

• The SiC hetero-polytypes are employed to design the impact ionization avalanche transit-time diodes (IMPATTDs).

• The 4H/6H-SiC hetero-polytype IMPATTDs imply advantages in power, efficiency and noise due to weak ionizing in materials.

• The noise electric field peaks arise from the strong ionizing layers while deviate from the in hetero-interfaces.

• The IMPATTDs with 3C/4H-SiC and 3C/6H-SiC hetero-polytype high-barriers encounter weak quantum effect.

Abstract

The SiC hetero-polytypes with perfect interfaces and no diffusion pollution are adopted to innovatively design the impact ionization avalanche transit-time (IMPATT) diodes. The performance of DC, large-signal and noise of the proposed diodes operating at the atmospheric low-loss window frequency 0.85 THz are estimated via numerically solving the fundamental device equations with and without quantum correction incorporated the tunnel and density-gradient of carriers. The influence from SiC hetero-polytype barriers and material properties on the performance of IMPATT diodes is analyzed. The advantages in power, efficiency and noise generating in the diodes of 4H/6H–SiC hetero-polytypes can be due to high critical breakdown electric field strength and weak ionizing in 4H–SiC and 6H–SiC. However, small power and heavy noise emerging from the devices of 3C/4H–SiC and 3C/6H–SiC hetero-polytypes can be owing to low critical breakdown electric field strength and strong ionizing in 3C–SiC. The noise electric field peaks arising from the strong ionizing layers while deviating from the interfaces in hetero-polytypes are illustrated. The evident quantum effect on the diodes without 3C–SiC while the slight effect on the devices included 3C–SiC are attributed to low-barriers embedded in the former diodes while high-barriers involved in the latter devices, respectively.

Introduction

The SiC-based hetero-structures and hetero-polytypes have attracted extensive attention, since they can be employed to control the electric field distribution, to modify the generation and transport of carriers as well as to adjust the heat transfer in semiconductor devices for improving performance. The 3C/4H–SiC, 3C/6H–SiC and 4H/6H–SiC hetero-interfaces, which are fabricated by the techniques of molecular beam epitaxy, hot-wall chemical vapor deposition, sublimation epitaxy in a vacuum, are illustrated as the interface transition regions of atomically flat observed by the high-resolution transmission electron microscopy (HRTEM) [1,2]. This indicates that the high-quality SiC hetero-polytypes can be grown by the existing mature methods. The two-dimensional electron gases (2DEGs) were demonstrated in the 3C/4H–SiC and 3C/6H–SiC interfaces [3], which implies that the perfect interfaces in SiC hetero-polytypes can be achieved. It reveals that the SiC hetero-polytypes can be utilized to design high-performance devices such as impact ionization avalanche transit time diodes (IMPATTDs), high electron mobility transistors (HEMTs), etc. In addition, the explorations on electric characteristics such as energy band offset [4,5] and optical properties such as photoluminescence [6] of the SiC hetero-polytypes lay the necessary foundation for the follow-up investigations. The excellent performance such as high-power and high-efficiency from the IMPATTDs and mixed tunneling avalanche transit time diodes (MITATTDs) designed by GaN-based, SiC-based homo- and hetero-structures have inspired keen research interests [[7], [8], [9], [10]], for developing the cost-affordable, operation at room temperature, two-terminal solid-state terahertz (THz) power oscillators and amplifiers available in radar, biomedicine detection etc. In order to overcome the power and efficiency degradation as well as the frequency shift encountered in homo-structural devices due to tunnel, taking the advantages of material, feasibility and complexity of the preparation process into account, the SiC hetero-polytypes with perfect interfaces and no diffusion pollution have been proposed to design the MITATTDs in our recent paper [11]. The tunnel effect on direct current (DC) and small-signal characteristics is implied as weak influence on the performance of the diodes included 3C–SiC, it is different from those of homo-structural diodes illustrated in literatures [7,12]. In this paper, the simulations on the DC, large-signal and noise properties of the SiC hetero-polytype IMPATT diodes running at 0.85 THz, are respectively performed by incorporating quantum correction associated with the tunnel and density-gradient framework and by taking only the drift-diffusion into account, in order to explore the device characteristics and the approach for constructing the high-performance diodes.