Theoretical Performance Analysis of InN-Based Double Channel High Electron Mobility Transistors (DHEMTs)

Introduction 1-7

Motivation and Objectives

Recently, polarization effect on carrier confinement and calculation of 2DEG concentration in InN-based double heterostructure have been reported by 1-lasan et al. Advances have also been made to investigate the 2DEG properties of InN-based DHEMTs in our previous work [ 25 ].

Outline of Dissertation

Streit, “Experimental and Theoretical Characteristics of High Performance Pseudomorphic Double Heteroj unction InAlAs/1no 7Ga03As/InAlAs HEMTs,” IEEE Trans. Maezawa, “Investigation of current collapse in AlGaN/GaN HEMTs induced by bias stress”, IEEE Trans.

Theory of 111-Nitride DHEMTs 8-25

ElI-Nitride DHEMT Characteristics

• Critical Thickness
• Properties of InN/InGaN/InN Heterostructure

Operation Principle of DHEMTs

A detailed discussion of the electronic properties of two-dimensional systems can be found in ref. A detailed study of the channel formation mechanism and the distribution of charges in the channel is presented. Doping is a very important parameter for introducing the carriers into the channel of the heterostructure devices.

The average distance of the 2DEGs inside the quantum well from the top heterointerface is shown in Fig. 4.9 Average distance of the 2DEGs from the top heterointerface for the proposed 50 nm well width in N-based DHEMT shown. A low-temperature mobility map as a function of the 2DEG field carrier (n5) is shown in Fig.

The peak electron concentration decreases with the increase of x and this is due to decrease of the. However, thermal effects are pronounced in the fabricated DHEMTs due to the low thermal conductivity of the sapphire substrate.

Modeling of Dl-IEMTs

• Equivalent Circuit Based Model
• Physics Based Model

Transport Model for Ill-Nitride DHEMTs

• Drift-Diffusion Model
• Thermodynamic Model
• Impact Ionization Model

Introduction

To develop advanced InN-based semiconductor devices, a thorough investigation based on device physics is necessary to provide a better understanding of the device operation. The developed model is used to study the impact of device performance on various technological parameters.

Device Structure

However, for the device investigation carried out in this thesis, the physics-based approach to charge control investigation in the double heterostructure InGaN/InN/InGaN is carried out by self-consistently solving the Schrödinger equation in combination with the Poisson equation, taking into account the spontaneous and piezoelectric polarization. Effects.

Charge Control Model

• One Dimensional Self Consistent Calculation
• Polarization Effects and Interface Model
• Average Distance of the 2DEGs from Top Heterointerface

The effect of the polarization charge at the bottom InN/JnGaN can thus be considered completely screened. This assumption is reasonable because most of the electrons are occupied in the first three subbands [I, 2]. This is due to the decrease of piezoelectric polarization-induced charges with little effect of the increase of spontaneous polarization-induced charges.

This variation of slab carrier concentration is due to the increase in conduction band discontinuity (E) of the top heterointerface with the gate voltage. These parameters are also found by calculating the average distance of the 2DEG from the top heterointerface in section 4.2.5. As the wave function moves closer to the interface of the 2DEG, the scattering from the interface roughness becomes more apparent.

Furthermore, the inter-subband dispersion also increases due to the reduction of the inter-subband gap with the increases in plate charge density. To realize the performance of the proposed InN-based DHEMTs, this chapter focuses on the DC characteristics, i.e.

Fig. 3.2 Schematic representation of the quasi-2D FET model implemented for current calculation in DHEMT

Quasi-2D Model for Calculation of Current

Transconductance Model

Hsieh, Hsin-Chu "Numerical Analysis of Non-Equilibrium Electron Transport in A1GaAs/InGaAs/GaAs Pseudornormorphic MODFETs," IEEE Trans. Morkoc, "Spontaneous polarization and piezoelectric field in GaN/AIGaN quantum wells: impact on the optical spectra," Phys. Spontaneous and piezoelectric polarization effects on the output characteristics of AIGaN/GaN heterojunction modulation doped FETs,” IEEE Trans.

Gupta, “An accurate charge control model for spontaneous and piezoelectric polarization-dependent two-dimensional electron gas sheet charge density of lattice-mismatched AIGaN/GaN HEMTs,” Solid-State Electronics , vol. Shealy, “Charge-Induced Two-Dimensional Electron Gases of Spontaneous and Piezoelectric Polarization in N- and GaN-Face AlGaN/GaN Heterostructures,” J. Yamamoto, “Two-Dimensional Electron Gas in InN-Based Heterostructures: Effects of Spontaneous and Piezoelectric Polarization, " Solid-State Electronics, vol.

Carnez, “Modeling of a submicrometer gate field-effect transistor including the effects of non-stationary electronic dynamics,” J. Cappy, “Noise modeling in a two-dimensional submicrometer gate electron-gas field-effect transistor,” IEEE Trans.

2DEGs Transport Properties 37-57

Carrier Control Characteristics

• Mechanism of Channel Formation and Distribution of Charges in the
• Composition Dependent Potential Profile and Carrier Concentration
• Variation of 2DEG Sheet Carrier Density with Gate voltage
• Variation of 2DEG Sheet Carrier Density with Doping Concentration
• Average Distance of 2DEG from Top 1-leterointerface

At a gate voltage, Vg=O.4 V (near threshold) only the bottom channel is conducted, where the carriers are mainly confined to the bottom interface of the well as shown in Fig.4.I. Because the carriers are localized near the bottom heterointerface, smaller gate capacitance is obtained due to the increased separation between metal gate and the 2DEG density. This high slab carrier density is due to the quantum confinement effect caused by the large conduction band shift of 2.2 eV and a large polarization-induced slab charge density due to the lattice mismatch between InGaN barrier and InN channel material [4].

The value of the shell carrier concentrations is greater than that for GaAs-based [51 and GaN-based [61 double heterostructure system. The effect of In mole fraction of the upper 1n,Ga1.N barrier layer on the potential profile is shown in Fig. The effect of changing In mole fraction (x) of the upper InGa1.N barrier layer on the distribution of carriers in the channel is shown in Fig.4.5.

The calculated sheet charge density of electrons in the proposed structure as a function of the gate voltage for different values ​​of In content (x) of the InGa,N barrier layer is shown in Fig. Thus one needs to find the optimal pit width for high speed operation of the DHEMT devices [5.

Fig. 4. 1 Calculated energy band diagram and electron distribution in the channel for proposed InN based DHEMT at gate bias, Vg = -0.4 V

Mobility Analysis

• Scattering Mechanisms in InN-Based DHEMTs
• Dislocation Scattering
• Ionized Impurity Scattering
• Alloy Disorder Scattering
• Interface Roughness Scattering
• Phonon Scattering
• Overall Mobility

These dislocations originate from the seed layer at the interface of the substrate and lnGaN and grow toward the surface without termination. The Fourier transform of the shielded potential experienced by the 2DEG due to a differential charge element dQ = p,dz located at a distance z from the interface is given by [3]. The spirit of the HEMT 2DEG is a spatial separation of the 2DEG from the ionized donors, reducing scattering and improving electron mobility.

Background impurity densities cannot be the source of the 2DEG electrons, as their concentration is too low to provide the high density 2DEG densities observed. Although the center of the 2DEG is in the binary material InN, there is a penetration of the wave function in the ternary InGaN barrier. The peeling of the wave function towards the interface can partially explain the decrease of the mobility when the plate charge density increases.

The expression of the mobility limited by the polar optical phonon scattering is given by Ridley as [17]. Then from this average relaxation time the mobility of the material can be easily obtained.

Fig. 4.10. Scattering processes limiting the 2DEGs mobility in InGaN/InN/InGaN heterostructures at 77K

Velocity Field Characteristics

The velocity reduction for higher electron mobility at smaller electric fields can be attributed to the result of the appearance of polar optical emissions as the electrons are heated rapidly due to the higher mobility. Walter, "On the charge control of the two-dimensional electron gas for analytical modeling of HEMTs." IEEE Electron Device Letter, vol. Sakaki, "Mobility of the two-dimensional electron gas at selectively doped n-type AlGa1 .As/GaAs heterojunctions with controlled electron concentrations.".

As the gate-to-source voltage (VGS) is increased from the threshold voltage, the depth of the potential well at the top heterointerface increases, resulting in the higher plate carrier concentration and higher drain current. The peak velocity of the carrier for the proposed device was found to be 4.95x10 cmsec at the field of 57.5 kV/cm. This velocity reduction for higher electron mobility at smaller electric fields can be attributed to the result of the occurrence of polar optical emissions as the electrons are heated rapidly due to the higher mobility.

These parameters are very essential for the development of device performance at high frequencies and should be studied in the future. Accurate device modeling is the first step to accurately design monolithic microwave integrated circuits (MMICs).

Fig: 4.12 Velocity-field characteristics of the proposed InGaN/lnN/lnGaN based DHEMT.

Performance of DHEMTs 58-6 1

Current-Voltage Characteristics

The calculated current-voltage characteristics for several gate biases for the DHEMT device of gate length 0.1 .im are shown in Fig. ID increases linearly with increasing VDS in the region of low longitudinal field (linear region) until fixation. The drain current also increases as V6.5 increases because as the gate-to-source voltage increases the sheet carrier concentration increases.

The maximum discharge current is found to be 1.325 A/mm for the proposed DHEMT at VGS =1.5V for different values ​​of the discharge-source voltage. The main reason for this increase is due to the increased channel carrier density from the dual heterostructure system. A similar increase in maximum drain saturation current was also reported in double heterostructure based GaN HEMT by Chen et al.

The variation of drain current with gate bias for 0.1tm gate-length InGaN/lnN/InGaN DHEMTs is depicted in Fig. This high value of drain saturation current makes InN-based DHEMT extremely attractive for microwave and millimeter wave applications.

Fig. 5.2 Transfer characteristics of the proposed InN-based double channel HEMT with VDs = 4 V

Transconductance Characteristics

Asif khan, "AIGaN/GaN/AIGaN double heterostructure for high power Ill-N field effect transistors," Applied Physics Lett., vol. Kettenib, 'Investigation of growth and electrical performance of double heterostructure AIGaN/GaN/AIGaN field effect transistors,' Phys.

Conclusions and Future Work 62-65

Future Work

This dissertation presented a detailed study about one-dimensional theoretical numerical modeling and performance evolution of InN-based DHEMT for high-speed and high-frequency applications. In this work, the DC characteristics, i.e., 1-V characteristics and transconductance are calculated by quasi-modeling (21), but high-frequency parameters such as cutoff frequency and peak output power are not calculated. The total channel current for various bias conditions is determined, which is extremely exciting, but the breakdown voltage, which is a vital limiting device performance parameter, is not determined.

Hydrodynamic simulation, taking into account self-heating effects and carrier velocity overshoot, should be performed for DHEMTs with submicron gates for high-frequency operation. In the simulation scheme used in this study, the isothermal condition is applied during the calculations. Using the hydrothermal simulation, the heat generation in any part of the device can be simulated and taken into account later in the design of the device.

Deng, "A novel InxGa.N/InN heterostructure field-effect transistor with extremely high two-dimensional electron gas sheet density." Asif khan, "AlGaN/GaN/AIGaN double heterostructure for high power Ill-N field effect transistors," Applied Physics Lett., vol.