BREAKTHROUGH CMOS N-Type Diamond Transistors

Diamond CMOS needs symmetrical doping control like we have for semiconductor silicon and diamond n-MOS is needed. The n-channel diamond MOSFETs are demonstrated. This work will enable the development of energy-efficient and high-reliability CMOS integrated circuits for high-power electronics, integrated spintronics, and extreme sensors under harsh environments.

Currently, p-channel diamond MOSFETs have been extensively developed and a routine fabrication process has been established. Owing to the lack of diamond n-MOSs, a complementary circuit has been reported to be accomplished using diamond p-MOSs and III-nitride n-MOSs. Although this is a promising strategy, all-diamond CMOS is the ultimate pursuit to fully exploit the figure-of-merit of diamond, particularly for electronics that operate under harsh environments (high temperatures and strong radiation).

Above – MOSFETs based on phosphorous doped n-type diamond and the electrical characteristics with temperatures up to 573 K. A) Schematic of the MOSFETs. The n+ diamond layer is used to reduce the source and drain contact resistance. The n− diamond layer serves as the channel. B) Optical image of the diamond MOSFETs. C) Transistor properties at 300, 423, and 573 K. The drain current increases by nearly four orders of magnitude from room temperature to 573 K.

n-type channel diamond MOSFETs were demonstrated on phosphorus-doped homoepitaxal (111) diamond epilayer. The n-type (111) diamond epilayer was grown based on a step-flow nucleation mode, enabling the precise control of the crystal quality and the donor distribution. The n-MOSFET showed a high mobility ≈150 cm2 V−1 s−1 at 573 K, a significant feature over other wide-bandgap semiconductors at high temperatures. The excellent high-temperature performance offers the route to develop diamond CMOS circuits for high-power electronics, integrated spintronics, and extreme sensors under harsh environments.

N-type diamonds can stabilize the negatively charged nitrogen-vacancy (NV−) state, greatly improving sensitivity. Thus, diamond CMOS-integrated NV centers are favorable for the development of diamond spin electronics that require dedicated controllability and integrity to scale up the quantum sensing protocol. The deep nature of the phosphorus in diamond benefits the generation of surface p-type conductivity in a lightly phosphorus-doped diamond epilayer with hydrogen termination. Thus, a diamond CMOS based on a planar process on lightly doped n-type diamond can be achieved. By using MEMS technology to engineer the band structure, the performance of n-type diamond MOSFETs can be further improved. This study sheds light on monolithically integrated diamond chips, in which electronics, spintronics, and sensors are based on diamond.

Diamond holds the highest figure-of-merits among all the known semiconductors for next-generation electronic devices far beyond the performance of conventional semiconductor silicon. To realize diamond integrated circuits, both n- and p-channel conductivity are required for the development of diamond complementary metal-oxide-semiconductor (CMOS) devices, as those established for semiconductor silicon. However, diamond CMOS has never been achieved due to the challenge in n-type channel MOS field-effect transistors (MOSFETs). Here, electronic-grade phosphorus-doped n-type diamond epilayer with an atomically flat surface based on step-flow nucleation mode is fabricated. Consequently, n-channel diamond MOSFETs are demonstrated. The n-type diamond MOSFETs exhibit a high field-effect mobility around 150 cm2 V−1 s−1 at 573 K, which is the highest among all the n-channel MOSFETs based on wide-bandgap semiconductors.

The development of diamond growth technologies, power electronics, spintronics, and microelectromechanical system (MEMS) sensors operatable under high-temperature and strong-radiation conditions, the demand for peripheral circuitry based on diamond CMOS devices has increased for monolithic integration. P-type diamonds are readily accessible through bulk boron doping or surface transfer doping of a hydrogen-terminated diamond surface.