[Paper Review] Analytical Modeling and Design of Gallium Oxide Schottky Barrier Diodes Beyond Unipolar Figure of Merit Using High-k Dielectric Superjunction Structures

Saurav Roy, Arkka Bhattacharyya+1 more|arXiv (Cornell University)|Aug 1, 2020

Ga2O3 and related materials12 references8 citations

TL;DR

This paper proposes a high-k dielectric superjunction structure for β-Ga₂O₃ Schottky barrier diodes to overcome the unipolar figure of merit (FOM) limit. By using conformal mapping and TCAD simulations, it achieves a 4× improvement in FOM—reaching 40 GW/cm²—through optimized aspect ratio (10), dielectric constant (300), and width ratios, enabling 20 kV breakdown voltage at 10 mΩ·cm² on-resistance.

ABSTRACT

This work presents the design of beta-Ga2O3 schottky barrier diode using high-k dielectric superjunction to significantly enhance the breakdown voltage vs on-resistance trade-off beyond its already high unipolar figure of merit. The device parameters are optimized using both TCAD simulations and analytical modeling using conformal mapping technique. The dielectric superjunction structure is found to be highly sensitive to the device dimensions and the dielectric constant of the insulator. The aspect ratio, which is the ratio of the length to the width of the drift region, is found to be the most important parameter in designing the structure and the proposed approach only works for aspect ratio much greater than one. The width of the dielectric layer and the dielectric constant also plays a crucial role in improving the device properties and are optimized to achieve maximum figure of merit. Using the optimized structure with an aspect ratio of 10 and a dielectric constant of 300, the structure is predicted to surpass the b-Ga2O3 unipolar figure of merit by four times indicating the promise of such structures for exceptional FOM vertical power electronics.

Motivation & Objective

• Overcome the intrinsic limit of β-Ga₂O₃ Schottky barrier diodes constrained by the unipolar figure of merit (FOM).
• Address the challenge of p-type doping deficiency in β-Ga₂O₃ that prevents conventional superjunction implementation.
• Enable high breakdown voltage and low on-resistance trade-off using dielectric superjunction structures with high-k materials.
• Develop an analytical model incorporating conformal mapping to accurately predict electric field distribution in asymmetric lateral structures.
• Optimize device geometry (aspect ratio, width ratios, dielectric constant) for maximum FOM using both analytical modeling and TCAD simulation.

Proposed method

• Developed an analytical model solving 2D Poisson’s equation in both semiconductor and dielectric regions using conformal mapping to handle fringing fields in asymmetric lateral structures.
• Applied conformal mapping to transform the complex geometry of the dielectric superjunction into a simpler domain for analytical solution of electrostatic potential and electric field.
• Used TCAD Sentaurus simulations to validate the analytical model and optimize device parameters under realistic conditions.
• Systematically varied key parameters: aspect ratio (L/W), semiconductor-to-dielectric width ratio (W_S/W_D), and dielectric constant (ε_r) to identify optimal configurations.
• Calculated the figure of merit (FOM) as BV²/R_on to evaluate performance beyond the unipolar FOM of β-Ga₂O₃.
• Explored the dependence of breakdown voltage and on-resistance on dielectric constant and geometric ratios to identify performance saturation points.

Experimental results

Research questions

• RQ1 Can a dielectric superjunction structure in β-Ga₂O₃ Schottky diodes surpass the unipolar FOM limit through electric field engineering?
• RQ2 How does the aspect ratio (length-to-width of drift region) affect the breakdown voltage and FOM in lateral dielectric superjunction SBDs?
• RQ3 What is the optimal semiconductor-to-dielectric width ratio (W_S/W_D) for maximizing breakdown voltage at a given dielectric constant?
• RQ4 How does the dielectric constant influence the breakdown voltage and FOM, especially in relation to aspect ratio?
• RQ5 To what extent can conformal mapping accurately model the fringing electric fields in asymmetric lateral dielectric superjunction structures?

Key findings

• The dielectric superjunction structure enables a 4× enhancement in the figure of merit (FOM) compared to the unipolar FOM of β-Ga₂O₃, achieving 40 GW/cm².
• An aspect ratio of 10 is required to realize significant performance gains; for aspect ratios less than one, no benefit over conventional SBDs is observed.
• With a dielectric constant of 300, a breakdown voltage of 20 kV is achieved at an on-resistance of 10 mΩ·cm², demonstrating exceptional power device potential.
• The optimal semiconductor-to-dielectric width ratio (W_S/W_D) is 0.2 for a dielectric constant of 300 and aspect ratio of 10, with a narrow range of optimal values for high-k materials.
• Breakdown voltage saturates at lower dielectric constants for low aspect ratios, but remains tunable up to higher values when aspect ratio is 10.
• A strong agreement between the analytical model and TCAD simulations confirms the model's accuracy in predicting field distribution and device performance in asymmetric structures.