On the Modeling of the Donor/Acceptor Compensation Ratio in Carbon-Doped GaN to Univocally Reproduce Breakdown Voltage and Current Collapse in Lateral GaN Power HEMTs.

Nicolò Zagni,Alessandro Chini,Paolo Pavan,Giovanni Verzellesi,Francesco Maria Puglisi

doi:10.3390/mi12060709

Nicolò Zagni, Alessandro Chini + Show 3 more

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https://doi.org/10.3390/mi12060709

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Abstract

The intentional doping of lateral GaN power high electron mobility transistors (HEMTs) with carbon (C) impurities is a common technique to reduce buffer conductivity and increase breakdown voltage. Due to the introduction of trap levels in the GaN bandgap, it is well known that these impurities give rise to dispersion, leading to the so-called “current collapse” as a collateral effect. Moreover, first-principles calculations and experimental evidence point out that C introduces trap levels of both acceptor and donor types. Here, we report on the modeling of the donor/acceptor compensation ratio (CR), that is, the ratio between the density of donors and acceptors associated with C doping, to consistently and univocally reproduce experimental breakdown voltage (VBD) and current-collapse magnitude (ΔICC). By means of calibrated numerical device simulations, we confirm that ΔICC is controlled by the effective trap concentration (i.e., the difference between the acceptor and donor densities), but we show that it is the total trap concentration (i.e., the sum of acceptor and donor densities) that determines VBD, such that a significant CR of at least 50% (depending on the technology) must be assumed to explain both phenomena quantitatively. The results presented in this work contribute to clarifying several previous reports, and are helpful to device engineers interested in modeling C-doped lateral GaN power HEMTs.

Highlights

Carbon (C) doping is a common technological solution to reduce buffer conductivity and increase breakdown voltage (V BD ) in lateral gallium nitride (GaN)-based power transistors [1,2]
In typical undoped GaN layers used as buffer in high electron mobility transistors (HEMTs), the position of the Fermi level is such that both acceptor and donor traps are likely to form
High unintentional C doping concentrations can likely occur for metal-organic chemical vapor deposition (MOCVD)-grown, intentionally Fe-doped HEMTs for RF applications, where C incorporation comes as an inevitable consequence of the growth processing conditions [30]

Summary

Introduction

Carbon (C) doping is a common technological solution to reduce buffer conductivity and increase breakdown voltage (V BD ) in lateral gallium nitride (GaN)-based power transistors [1,2]. Several works, discussing either simulation or experimental results, indicate the occurrence of partial “auto-compensation” between the dominant deep acceptor traps, generally attributed to CN levels, and the concomitantly introduced (i.e., non-pre-existing) shallow donors, which reduce the effective concentration of acceptor traps well below the level of the introduced C concentration (especially in the case of extrinsic C doping) [4,9,10,11,12,13,14,15] These aspects call for the correct modeling of C-related trap states in GaN transistors when performing device simulations to investigate important performance-limiting

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