Abstract
The discovery of the extremely shallow amorphous boron-crystalline silicon heterojunction occurred during the development of highly sensitive, hard and robust detectors for low-penetration-depth ionizing radiation, such as ultraviolet photons and low-energy electrons (below 1 keV). For many years it was believed that the junction created by the chemical vapor deposition of amorphous boron on n-type crystalline silicon was a shallow p-n junction, although experimental results could not provide evidence for such a conclusion. Only recently, quantum-mechanics based modelling revealed the unique nature and the formation mechanism of this new junction. Here, we review the initiation and the history of understanding the a-B/c-Si interface (henceforth called the “boron-silicon junction”), as well as its importance for the microelectronics industry, followed by the scientific perception of the new junctions. Future developments and possible research directions are also discussed.
Highlights
Initiation and History of Boron-Silicon Junctions and Importance ofSi-Based Junctions/Diodes in MicroelectronicsThe first report about an ultra-shallow rectifying junction created by a pure boron atmospheric/low-pressure chemical vapor deposition (AP/LPCVD) on crystalline n-type silicon surface was published in 2006 [1]
Since 2006 a significant amount of research has been completed in the following directions: (1) optimization of the critical junction creation process, i.e., the chemical vapor deposition (CVD) of amorphous boron on n-type crystalline silicon; (2) device characterization and design optimization for a variety of applications; and (3) rendering the PureB process CMOS-compatible
To gain insight into the preparation processes and the structural and electronic properties of the boron-silicon heterojunction, we modeled the decomposition of B2 H6 molecules and the deposition of BHn (n = 1–4) molecular/radicals on a Si substrate at the early stages of the PureB processes [10,25,26], and Amorphous pure boron (a-B)/crystalline Si substrates (c-Si) interfaces [10,27]
Summary
The first report about an ultra-shallow rectifying junction (diode) created by a pure boron atmospheric/low-pressure chemical vapor deposition (AP/LPCVD) on crystalline n-type silicon surface was published in 2006 [1]. The idea of the delta-doped p+ layer playing any significant role in the junction formation was completely abandoned when it was demonstrated that similar excellent electrical properties could be achieved by boron CVD on n-type crystalline silicon substrates at temperatures as low as 400 ◦ C, at which no doping of boron in silicon is expected [7]. A first-principles quantum mechanics molecular dynamics simulation showed a very strong electric field across the a-B/c-Si interface systems where the charge transfer occurred mainly from the interface Si atoms to the neighboring B atoms This electric field appeared to be responsible for the creation of a depletion zone in the n-silicon, resulting in a rectifying junction formation. The PureB Process and Characterization of the Boron-Silicon Junction as a Radiation Detector
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