Traps and Surfaces: SRH Recombination | Solid State Physics 6.6

Direct recombination should kill a silicon carrier in about 21 ms, yet real silicon gives up in a microsecond. The shortcut is a trap near the middle of the band gap, a stepping stone that lets an electron and a hole meet in two small steps without needing a photon. We derive the lifetime from a capture cross-section and trap density, see why one stray atom in five hundred million is enough, and meet the full Shockley-Read-Hall expression. Then the surface, a whole plane of dangling bonds, gets its own recombination velocity, and we close the last two bills of the series. Chapters 0:00 Two bills still on the table 0:37 1952: Robert Hall and a factor of two 1:26 A trap in the gap, step by step 2:26 Where should a trap sit to kill fastest? 3:09 Counting traps in a cylinder 4:17 Plugging in the numbers 5:15 The full Shockley-Read-Hall result 6:08 The second bill: the surface 6:29 Dangling bonds 6:46 Surface recombination velocity 7:25 A thin wafer 7:48 Settling the bill from episode four 8:16 The history of surface states 9:11 Six episodes, one chain 9:41 Three takeaways 10:05 Every bill is paid Reference: Donald A. Neamen, *Semiconductor Physics and Devices: Basic Principles*, 4th ed., Chapter 6 (excess carriers). Historical sources: Shockley & Read, "Statistics of the Recombinations of Holes and Electrons", Phys. Rev. 87, 835 (1952): https://journals.aps.org/pr/abstract/... · Hall, "Electron-Hole Recombination in Germanium", Phys. Rev. 87, 387 (1952): https://journals.aps.org/pr/abstract/... · Collins, Carlson & Gallagher, "Properties of Gold-Doped Silicon", Phys. Rev. 105, 1168 (1957): https://journals.aps.org/pr/abstract/... · Bemski, "Recombination Properties of Gold in Silicon", Phys. Rev. 111, 1515 (1958): https://journals.aps.org/pr/abstract/... · Bardeen, "Surface States and Rectification at a Metal Semi-Conductor Contact", Phys. Rev. 71, 717 (1947): https://journals.aps.org/pr/abstract/... · Atalla, Tannenbaum & Scheibner, "Stabilization of Silicon Surfaces by Thermally Grown Oxides", Bell System Technical Journal 38, 749 (1959): https://archive.org/details/bstj38-3-749 · Blakers et al., "22.8% efficient silicon solar cell", Appl. Phys. Lett. 55, 1363 (1989): https://openresearch-repository.anu.e... Previous episode: "Two Fermi Levels". Next chapter: the pn junction (episode title to verify). Narration: AI voice (ElevenLabs); music: AI-generated (Lyria).