Device Design Assessment of GaN Merged P-i-N Schottky Diodes

Abstract

Device characteristics of GaN merged P-i-N Schottky (MPS) diodes were evaluated and studied via two-dimensional technology computer-aided design (TCAD) after calibrating model parameters and critical electrical fields with experimental proven results. The device’s physical dimensions and drift layer concentration were varied to study their influence on the device’s performance. Extending the inter-p-GaN region distance or the Schottky contact portion could enhance the forward conduction capability; however, this leads to compromised electrical field screening effects from neighboring PN junctions, as well as reduced breakdown voltage. By reducing the drift layer background concentration, a higher breakdown voltage was expected for MPSs, as a larger portion of the drift layer itself could be depleted for sustaining vertical reverse voltage. However, lowering the drift layer concentration would also result in a reduction in forward conduction capability. The method and results of this study provide a guideline for designing MPS diodes with target blocking voltage and forward conduction at a low bias.

Comprehensive Design and Numerical Study of GaN Vertical MPS Diodes Towards Alleviated Electric Field Crowding and Efficient Carrier Injection

“…𝑅 𝑜𝑛1 = 𝑅 𝐷1 + 𝑅 𝐷2 + 𝑅 𝐷3 + 𝑅 𝑠𝑢𝑏 (11) where 𝜌 𝐷 is the resistivity of the drift layer, 𝜌 𝑠𝑢𝑏 is the resistivity of the substrate, 𝑊 𝐷 is the depletion width of the pn junction, 𝑃 is the width of the whole device, 𝑡 is the thickness of the drift layer, 𝑡 𝑠𝑢𝑏 is the thickness of the substrate, and 𝑍 is the width in the third dimension of the MPS diode. The forward voltage drop (𝑉 𝐹 ) at low current density 𝐽 𝐹 can be calculated by equations (12) and (13):…”

“…However, similar to the lateral GaN SBDs based on the AlGaN/GaN heterostructures, GaN vertical SBDs also suffer from reverse leakage issues due to the energy barrier lowering effect at high reverse bias condition. To achieve a decent device performance, several device architectures have been developed, such as junction barrier Schottky (JBS) diode [8], MPS diode [9] - [12], and trench metal-insulator-semiconductor barrier Schottky (TMBS) diode [13], [14], which are designed to move the peak electric field from the interface of the Schottky junction to the inside of the device at high reverse bias, leading to a higher breakdown voltage and a lower reverse leakage current.…”

“…Comprehensive Design and Numerical Study of GaN Vertical MPS Diodes towards Alleviated Electric Field Crowding and Efficient Carrier Injection fabricated with breakdown voltage up to 2 kV [9]- [11], the impact of the key design parameters as well as the working principles of GaN-based MPS diodes still remain to be explored systematically. Zhang et al investigated the impact of the lateral dimension of the Schottky regions on the device performance by assuming a fixed p-GaN thickness of 800 nm and p-doping concentration of 210 17 cm -3 [12]. However, during practical fabrication process, the p-GaN thickness and doping concentration may vary from the proposed values, which can result in a disparate impact from the lateral dimensions.…”

Review of Recent Progress on Vertical GaN-Based PN Diodes

“…For utilizing a high BV with low reverse leakage current of PNDs, high switching performance and low turn-on voltage of SBDs at the same time, novel device structures including the junction barrier Schottky (JBS) and merged PN Schottky (MPS) generate a combination of SBD and PND by the formation of p-type grid regions in the Schottky contact region. JBS or MPS devices possess the characteristics of forward conduction of SBDs and reverse blocking of PNDs and are expected to have better switching performance and higher reverse voltage than conventional PNDs and SBDs, respectively [35].…”