Betavoltaic and photovoltaic energy conversion in three‐dimensional macroporous silicon diodes

Abstract

A three‐dimensional p–n diode structure is presented for the generation of energy via photovoltaic and betavoltaic modes of operation. Macroporous Silicon (MPS) has a large degree of internal surface area and its vertically oriented pores, which extend deep into the bulk of the Si substrate, allow for the creation of three‐dimensional structures. In this device the MPS will not only serve as a means for creating 3D diode structures, it will also serve as a host matrix for a tritium isotope which emits energetic beta particles. By varying electrochemical etching conditions and using a prepatterning technique, 1.1 μm diameter pores with a spacing of 2.5 μm were achieved. The p–n junction was created using a rapid thermal process (RTP) which relies on the diffusion from an n‐type solid source into the MPS. To ensure the quality of the diode structure, devices were tested using a light source which resulted in a photovoltaic response. Finally, betavoltaic operation was demonstrated by exposing devices to a tritium gas source. The average energy conversion efficiency of the first generation 3D diode was one order of magnitude higher than that of a similar planar device. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Conformal P‐N junctions in macroporous silicon for photovoltaic energy conversion

“…6(a) fill factors > 70% were achieved. This is an improvement upon generation I devices [12,13] and approaches the fill factor of today's c-Si cells. To further characterize the photovoltaic spectral response, the diodes were illuminated with a simulated AM 1.5 solar spectrum.…”

“…This was previously achieved via solid source diffusion and has been reported in [12]. In the present work, proximity rapid thermal diffusion (PRTD) [14][15][16], was adopted as a better alternative [13]. Further development of this process reported herein has resulted in better control of the diffusion process and more consistent junction formation in the pores and ultimately improved device performance.…”

“…In previous work, we have reported 3-D PSi p-n diodes for use in betavoltaic energy conversion [12,13]. By adjusting the PSi film's properties these diodes can be tailored for photovoltaic energy conversion.…”

“…Etching conditions were similar to those used in [13]. Figure 1 shows a thin randomly formed MPS film and a thick pre-patterned MPS film.…”

“…By adjusting the PSi film's properties these diodes can be tailored for photovoltaic energy conversion. Preliminary results obtained with macroporous silicon (MPS) layers as deep as 80 μm showed a promising photovoltaic response [12,13]. A newly developed proximity rapid thermal diffusion process based on reports from [14][15][16] allows for shallow, strongly doped regions which extend throughout the MPS matrix to form the final 3-D p-n diode.…”