A Three‐Dimensional Porous Silicon p–n Diode for Betavoltaics and Photovoltaics

Abstract

Modern society is experiencing an ever-increasing demand for energy to power a vast array of electrical and mechanical devices. As hydrocarbon resources dwindle, utilization of ample nuclear energy and abundant solar energy becomes more and more attractive. For 50 years, since the invention of the transistor, semiconductor devices that convert the energy of nuclear particles [1±5] or solar photons [6,7] to electric current have been investigated. However, conventional two-dimensional (2D) planar diode structures exhibit a number of inherent deficiencies that result in relatively low energy-conversion efficiencies. A unique three-dimensional (3D) porous silicon p±n diode has been developed to form the basis of a novel betavoltaic battery. Using tritium to demonstrate the proof-ofconcept, the 3D diode geometry demonstrated a tenfold enhancement of efficiency compared to that of the usual 2D betavoltaic device geometry. Given the similarity of the energyconversion physics for betavoltaic and photovoltaic devices, significant efficiency gains due to this 3D geometry might be expected for many types of photo detectors and solar cells. The 3D diode was constructed on porous silicon (PS), which consists of a network of pores formed by electrochemical anodization of silicon substrates. According to the pore size, PS is classified as microporous (£ 2 nm), mesoporous (2±50 nm), or macroporous (> 50 nm). Such porous morphologies define a very large internal surface area, [8,9] which retains most of the characteristics associated with planar surface geometries, particularly for macropores. [10,11] Numerous investigations have been done on the physical and chemical properties of this complex material. [8,9,12] Moreover, it has been demonstrated that PS components can be integrated into microelectronic circuits in order to construct practical devices. [13] To date, however, PS has only been used as an antireflection and surface-passivation layer [14,15] in photovoltaic devices. It is believed that this work reports the first construction of conformal p±n junctions in PS. PS diodes with a 3D p±n junction structure were created as illustrated schematically in Figure 1 (see Experimental for details). The continuous p±n junction can be visualized as a 2D ªsheetº that is deformed to produce a uniform p±n junction layer on every accessible surface of the pore space. The builtin voltage [16] of the diodes was estimated to be~0.8 V, assuming an n-dopant concentration of~5 10 18 cm ±3 and an abrupt p±n junction doping profile. The metallurgical junction was about 200 nm below the surface, and the estimated depletion width on the p-side of the junction was~1.4 lm. The efficacy of the pore anodization procedure was investigated by means of scanning electron microscopy (SEM

Amorphous silicon based betavoltaic devices

“…Furthermore, T is industrially available, relatively cheap and can be embedded, if needed, in a solid matrix. Recently, a new battery design has been proposed comprising a 3D porous silicon diode to increase the surface interaction between the active volume (containing T) and the semiconductor device to improve performances [3].…”

Self-irradiation enhanced tritium solubility in hydrogenated amorphous and crystalline silicon

“…[1][2][3][4][5][6][7] Radioactive isotope micropower sources (RIMS) offer a number of unique advantages including its high power density and long operation life. One of the daunting challenges for chip-scale RIMS applications is to develop a safe and cost-effective method of integrating radioactive material on-chip with minimal collateral contamination to surrounding microelectronics circuits or MEMS structures.…”

Betavoltaics using scandium tritide and contact potential difference

“…2,4,7,8 Tritium is a pure beta emitter producing energetic electrons with an average energy of 5.7 keV and a maximum energy of 18.6 keV. Considering that the threshold electron energy for disruption of the silicon lattice due to knock-on collisions is 20 keV, 9 tritium decay beta particles pose little radiation damage concern for on-chip energy conversion devices.…”

“…Tritium in the gaseous form has been used in self-power lighting and in betavoltaic applications. 1,4 However, the gaseous form of tritium has a low-power density of 87 W / cm 3 , not to mention the challenge of hermetic containment of tritium gas and associated hazard of tritium leakage. In this letter, we demonstrate a betavoltaic micropower source using high-density tritium metal hydride foils.…”

“…[1][2][3][4][5][6] A number of nuclear-toelectrical energy conversion integrations, which had been investigated previously, are receiving renewed attention and novel materials and modern microfabrication techniques are being introduced. 1, 3 In recent years, a series of studies have been reported on betavoltaics employing semiconductor pn junction using materials such as amorphous silicon, 2 porous silicon, 4 silicon carbide, 5,6 and gallium arsenide/nitride. 1 The efficiency and longevity of these battery structures rely on high-quality pn junctions, which are often susceptible to radiation damage and lack structural self-healing resiliency.…”