Low temperature epitaxial technology for GaN-based materials

band gap of GaN-based semiconductor materials covers the entire visible light band and has excellent physical and chemical properties, which makes it widely used in the fabrication of optoelectronic devices, power electronic devices, and radio frequency and microwave devices. Traditional GaN-based materials are usually epitaxially grown on hightemperature-resistant single-crystalline substrates such as sapphire, silicon, or silicon carbide using metal-organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), or hydride vapor phase epitaxy (HVPE). These epitaxial techniques usually use high temperature to crack the precursors involved in the reaction. With the deepening of informatization and intelligentization, the common demands for low-cost and flexibility of opto(electronic) devices have emerged. On one hand, the display technology is a key link to realize information exchange and intelligence. Moving towards an intelligent society requires further reduction of the display cost per unit area. At the same time, the wearable and portable flexible display technology also has broad application prospects. In addition, solid-state lighting has gradually penetrated into every corner of human life with the improvement of device performance. The application scenarios are rich and colorful. Judging from this, low-cost surface light sources will be a strong competitor for the next generation of lighting technology routes. On the other hand, reducing the fabrication cost of electronic devices per unit area also needs more attention in the future. For example, flexible electronic skin has broad and huge application prospects in artificial limbs, robotics, medical detection and diagnosis, etc., which has also spawned the demand for low-cost flexible sensors. It can be seen that the common requirements of the above applications for core components are low cost and flexibility, which is also one of the main development directions of the next generation of (opto)electronic devices. Amorphous substrates (such as glass, plastic, metal, polyethylene terephthalate (PET), polydimethylsiloxane (PDMS), etc.) that are cheap and easy to fabricate are ideal choices, but a significant disadvantage is that amorphous substrates cannot withstand high growth temperatures. Therefore, the need for low-temperature epitaxy of GaN-based materials has arisen, that is, a kind of epitaxy equipment that can use external electric field energy to crack the reaction precursor at low temperatures. So far, a variety of low-temperature epitaxial technologies have been developed based on the physical vapor deposition (PVD) and the chemical vapor deposition (CVD), and preliminary research results have been obtained. The PVD techniques include reactive magnetron sputtering, plasma-assisted MBE (PA-MBE), pulsed laser deposition (PLD), pulsed sputtering deposition (PSD), laser MBE (LMBE), etc. The CVD techniques include remote plasma CVD (RPCVD), migration enhanced afterglow CVD (MEA-CVD), remote plasma-enhanced MOCVD (RPEMOCVD), radical-enhanced MOCVD (REMOCVD), electron cyclotron resonance plasma-enhanced MOCVD (ECR-PEMOCVD), inductive coupled plasma MOCVD (ICP-MOCVD), etc. In this paper, the two types of low-temperature epitaxial technologies are introduced in detail, including the device structure, working conditions and related epitaxial growth results, and the characteristics of each type of technology are summarized. Finally, the development prospect of low temperature epitaxial technologies is prospected, and the focus of future research is pointed out. We hope this work can provide a useful reference for the low temperature epitaxy research of GaN-based materials.