arXiv subjects

Hongjia Bi

Publications and source records attributed to Hongjia Bi.

3 recordsLinked to original sources

arXiv2026

The boron-hydrogen-phosphorus tri-elements co-doped stable N-type single crystalline Diamond

Diamond is an outstanding semiconductor for extreme electronics, yet reproducible n-type doping remains a long-standing challenge. Here we demonstrate stable n-type single-crystal diamond grown in a single step by a precisely controlled boron-hydrogen-phosphorus co-doping strategy. Hall measurements yield electron concentrations up to 1.0*1019 cm-3 with a resistivity as low as 0.249 ohmic.cm. Secondary-ion mass spectrometry shows that tri-elements doping is the key for achieving n-type conductivity as the electron density exceeds the incorporated phosphorus concentration and is the same level of that of hydrogen and boron concentrations, supporting a donor mechanism beyond an isolated substitutional phosphorus or just boron-hydrogen co-doping. Temperature-dependent photoluminescence (PL) reveals this tri-elements codoping method induces the impurity band, and the donor level is quite shallow around 61.6 meV, consistent with the temperature dependent resistance measurements. Moreover, the co-doped diamond also exhibits strong ultraviolet emission near 270-285 nm, and the internal quantum efficiency is estimated to be 69.4%, while the undoped diamond or only boron doped diamond shows negligible UV emission. These results establish a practical route to low-resistance high luminous n-type diamond and its based chips.

physics.app-ph↗

arXiv2025

Excitonic Insulator and Possible Superfluid Based on Two-Dimensional Diamond

Recent research on excitonic insulator has progressed mainly based on narrow bandgap semiconductor or semimetal. Herein, we realize excitonic insulator based on two-dimensional (2D) wide band gap diamond with transition temperature as high as 220K. The resistance rises dramatically by more than three orders, which can be explained by the Bose-Einstein condensation (BEC) of excitons. While cooling down below transition temperature, the wavelength of the bound excitons caused by boron and nitrogen centers becomes highly overlapped, leading to BEC process. Furthermore, the variable range hopping mechanism is used to simulate the resistance as a function of temperature, which reveals the formation of excitonic insulator. When temperature drops down further, a sudden drop of resistance over three orders was observed around 60K, possibly due to the formation of non-equilibrium excitonic superfluid resulting from highly overlap of wavelength of the large density bound excitons at lower temperature. This study provides evidences for excitonic insulator and possible superfluid phase based on wide bandgap semiconductor.

quant-ph↗

arXiv2024

Possible High temperature Superconductivity above 200K mediated by Bose Einstein Condensation of exciton

Exciton mediated superconductor is a fascinating quantum phase of matter that occurs when excitons become the dominant excitation in materials, which is also very promising for high temperature superconductor. However, there is no experimental report of exciton mediated superconductivity. Herein, we realize exciton mediated superconductivity from exciton insulator, where the onset transition temperature can reach larger than 200 K. More profoundly, Bose-Einstein condensation (BEC) of exciton can facilitate the formation of exciton insulator and a transition happened from extremely high resistivity of 107 {\Omega} at 153.5 K to 100 {\Omega} at 125 K, indicating a superconducting transition. The resistance of exciton mediated superconductivity can not be absolutely reach zero possibly as a result of drag effect between electrons/holes and excitons. We reveal one rule for exciton mediated superconductivity is that the resistivity is an inverse linear function of the current through the BEC superfluid state, which should be ascribed to the Andreev-Bashkin effect, which reflects the coupling between the BEC state of exciton and Cooper pairs mediated by excitons. Furthermore, a record transition temperature above 200 K has been found for one superconducting sample, which shows the Josephson oscillation dominated by a pendulum-like equation caused by the quantum coupling between superconductor and BEC superfluid of exciton.

cond-mat.supr-con↗