Baikui Li

Schottky-on-heterojunction optoelectronic functional devices realized on AlGaN/GaN-on-Si platform

We demonstrated that the metal-AlGaN/GaN Schottky diode is capable of producing GaN band-edge ultraviolet (UV) emission at 3.4 eV/364 nm under forward bias larger than ~2 V at room temperature. The underlying mechanism of the hole generation/injection and electroluminescence (EL) processes in this Schottky-on-heterojunction light-emitting diode (SoH-LED) was discussed based on the impact ionization of surface states presented in the (Al)GaN barrier layer. By replacing the conventional ohmic drain with a semitransparent Schottky drain, we demonstrated an AlGaN/GaN high-electron-mobility light-emitting transistor (HEM-LET) in which the drain current and EL emission are controlled simultaneously by gate voltage. Switching operation up to 120 MHz was obtained in SoH-LED to demonstrate its potential in providing high-speed on-chip light sources on the GaN electronic device platform.

Characterization of Static and Dynamic Behaviors in AlGaN/GaN-on-Si Power Transistors With Photonic-Ohmic Drain

In this paper, static and dynamic performances of an AlGaN/GaN-on-Si power FET utilizing the integrated photonic-ohmic drain (PODFET) were systematically investigated. The operational mechanisms of the PODFET, including both the conditions of photon generation and the related physical processes, were explained. The dynamic switching tests were carried out under two types of hard switching conditions. With the photon generation and channel current inherently switched ON and OFF in synchronization, the dynamic performances of the PODFET can be significantly enhanced owing to photon pumping of deep electron traps. In addition, the generated photons were proved to be confined in proximity of the drain terminal without causing adverse effects on the device performances (e.g., the OFF-state leakage degradation).

Optical pumping of deep traps in AlGaN/GaN-on-Si HEMTs using an on-chip Schottky-on-heterojunction light-emitting diode

In this work, by using an on-chip integrated Schottky-on-heterojunction light-emitting diode (SoH-LED) which is seamlessly integrated with the AlGaN/GaN high electron mobility transistor (HEMT), we studied the effect of on-chip light illumination on the de-trapping processes of electrons from both surface and bulk traps. Surface trapping was generated by applying OFF-state drain bias stress, while bulk trapping was generated by applying positive substrate bias stress. The de-trapping processes of surface and/or bulk traps were monitored by measuring the recovery of dynamic on-resistance Ron and/or threshold voltage Vth of the HEMT. The results show that the recovery processes of both dynamic Ron and threshold voltage Vth of the HEMT can be accelerated by the on-chip SoH-LED light illumination, demonstrating the potentiality of on-chip hybrid opto-HEMTs to minimize the influences of traps during dynamic operation of AlGaN/GaN power HEMTs.

On-chip optical pumping of deep traps in AlGaN/GaN-on-Si power HEMTs

In this work, by using an on-chip Schottky-on-heterojunction light-emitting diode (SoH-LED) which is seamlessly integrated with the AlGaN/GaN high electron mobility transistor (HEMT), we studied the effect of on-chip light illumination on the de-trapping processes of electrons from both surface and bulk traps. Surface trapping was generated by applying OFF-state drain bias stress, while bulk trapping was generated by applying positive substrate bias stress. The de-trapping processes of surface and/or bulk traps were monitored by measuring the recovery of dynamic on-resistance Ron and/or threshold voltage Vth of the HEMT. The results show that the recovery processes of both dynamic Ron and threshold voltage Vth of the HEMT can be accelerated by the on-chip SoH-LED light illumination, demonstrating the feasibility of fully integrated opto-HEMTs to minimize the influences of traps during the dynamic operation of AlGaN/GaN power HEMTs.

Interface Engineering of Monolayer MoS2/GaN Hybrid Heterostructure: Modified Band Alignment for Photocatalytic Water Splitting Application by Nitridation Treatment

Interface engineering is a key strategy to deal with the two-dimensional (2D)/three-dimensional (3D) hybrid heterostructure, since the properties of this atomic-layer-thick 2D material can easily be impacted by the substrate environment. In this work, the structural, electronic, and optical properties of the 2D/3D heterostructure of monolayer MoS2 on wurtzite GaN surface without and with nitridation interfacial layer are systematically investigated by first-principles calculation and experimental analysis. The nitridation interfacial layer can be introduced into the 2D/3D heterostructure by remote N2 plasma treatment to GaN sample surface prior to stacking monolayer MoS2 on top. The calculation results reveal that the 2D/3D integrated heterostructure is energetically favorable with a negative formation energy. Both interfaces demonstrate indirect band gap, which is a benefit for longer lifetime of the photoexcited carriers. Meanwhile, the conduction band edge and valence band edge of the MoS2 side increases after nitridation treatment. The modification to band alignment is then verified by X-ray photoelectron spectroscopy measurement on MoS2/GaN heterostructures constructed by a modified wet-transfer technique, which indicates that the MoS2/GaN heterostructure without nitridation shows a type-II alignment with a conduction band offset (CBO) of only 0.07 eV. However, by the deployment of interface nitridation, the band edges of MoS2 move upward for ∼0.5 eV as a result of the nitridized substrate property. The significantly increased CBO could lead to better electron accumulation capability at the GaN side. The nitridized 2D/3D heterostructure with effective interface treatment exhibits a clean band gap and substantial optical absorption ability and could be potentially used as practical photocatalyst for hydrogen generation by water splitting using solar energy.

Impact of integrated photonic-ohmic drain on static and dynamic characteristics of GaN-on-Si heterojunction power transistors

In this work, static and dynamic characteristics of an AlGaN/GaN-on-Si power field-effect transistor (FET) with the integrated photonic-ohmic drain (POD) were systematically investigated. With the photon generation and channel current inherently switched ON and OFF in synchronization, dynamic performances (e.g. dynamic ON-resistance) of the PODFET can be significantly enhanced owing to photon pumping of deep electron traps. It is shown that the photons responsible for photon pumping of deep traps were confined in the proximity of the drain terminal without causing adverse effects on the device static performances (e.g. the OFF-state leakage degradation). Furthermore, the POD structure featured a robust tuning capacity on both breakdown voltage and threshold channel current for photon generation to the AlGaN/GaN power FET.

Enhancing dynamic performance of GaN-on-Si power devices with on-chip photon pumping

In this work, we report a feasible compact solution to enhance the dynamic performance of GaN-on-Si power devices by integrating a photon source into the drain terminal of a heterojunction field-effect transistor (FET). Photons can be generated from the photonic-ohmic drain (POD) synchronously with turning on of the channel current. These on-chip generated photons can optically pump the electron traps, consequently enhancing the dynamic performance of GaN power devices. Both static and dynamic characteristics of PODFET were systematically investigated. The dynamic performance (e.g. dynamic ON-resistance) of PODFET was significantly enhanced owing to photon pumping of electrons from deep surface/bulk traps during hard switching configurations. Photon induced adverse effects on the device performances (e.g. the OFF-state leakage degradation) was measured to be negligible for high-voltage devices (e.g. 600 V).

Switching Behaviors of On-Chip Photon Source on AlGaN/GaN-on-Si Power HEMTs Platform

The switching behavior of on-chip photon sources, i.e., the p-doping-free Schottky-on-heterojunction light-emitting diodes (SoH-LEDs), which can be seamlessly integrated into the AlGaN/GaN-on-Si power high electron mobility transistors platform is investigated. It is demonstrated that the electroluminescence (EL) from an interdigital SoH-LED can be switched at least up to 10 MHz, fulfilling the requirement of most power switching circuits. In order to evaluate the EL switching limit of SoH-LEDs, a quantitative analysis of the dependence of junction current on operating frequency at different dc biases is performed based on S-parameter characteristics. At a criterion of junction-current/input-current to 50%, the cutoff frequency of an interdigital SoH-LED is obtained to be 210 MHz at a forward bias of 4 V. This letter proves that the SoH-LED is adequately fast for being employed as an on-chip synchronous photon source in GaN power switching applications.