Mechanism of B diffusion in crystalline Ge under proton irradiation

Abstract

B diffusion in crystalline Ge is investigated by proton irradiation in thin layers with B delta doping under different fluences (1×1015–10×1015 H+/cm2), fluxes (6×1011–35×1011 H+/cm2 s), and temperatures of the implanted target (from −196 to 550 °C), both during and after irradiation. B migration is enhanced by several orders of magnitude with respect to equilibrium. Moreover, B diffusion is shown to occur through a point-defect-mediated mechanism, compatible with a kick-out process. The diffusion mechanism is discussed. These results are a key point for a full comprehension of the B diffusion in Ge

Mechanisms of boron diffusion in silicon and germanium

“…20 shows that the B diffusion is very similar in the two cases, suggesting that indeed the process is mainly driven by the energy deposited into nuclear elastic collisions, producing pointdefects, while ionization effects are negligible, if any. This was also confirmed by the evidence that B undergoes an enhanced diffusion also after ion irradiation, 108 as in this last case, ionization effects are truly absent.…”

“…The method consists in monitoring the broadening of a B delta (grown by MBE) during irradiation with light ions at different target temperatures. 108 By this way, we demonstrated the occurrence of radiation enhanced diffusion (RED) of B in Ge, several orders of magnitude larger than under equilibrium conditions. Some years ago, RED of B in Ge was actually proposed by Uppal and coworkers to explain the long tails occurring after B implantation in Ge at low energy, even if no further investigation was given.…”

“…[108][109][110] By comparing the diffusion of Ge, B and P under proton irradiation, Bracht and co-workers demonstrated that I-mediated diffusion (as in the B case) is favored under irradiation. 109 The key role of Is in B migration was also clearly shown through an independent approach, by investigating the diffusion of B under out of equilibrium conditions for point defect density, 108,110 as described in Sec IV B. In fact, as B is such a slow diffuser, the first experimental studies of its migration mechanism were been limited to a restricted range of very high temperatures and very long times.…”

Isovalent doping and the CiOi defect in germanium

“…Although germanium (Ge) was implemented in the first transistor commencing the solid state electronics era silicon (Si) prevailed for applications in microelectronics, photovoltaics and sensors for many decades due to its high quality crystal growth technology and advantageous native oxide [1][2][3][4][5][6][7][8][9][10][11][12]. In the past few years materials with advantageous physical properties (e.g.…”

“…In the past few years materials with advantageous physical properties (e.g. higher carrier mobilities, low dopant activation temperatures and smaller band-gap) such as germanium (Ge) are becoming increasingly important [1][2][3][4][5][6][7][8][9][10][11][12]. The consideration of alternative substrates is mainly due to the high-k gate dielectric materials, which have effectively eliminated the requirement of a good quality native oxide in advanced nanoelectronic devices [1].…”