Periodic structure is observed in the tunneling current from heavily doped ($n^{+}$) GaAs through ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ into lightly doped ($n^{-}$) GaAs at 1.6 K in magnetic fields large enough for magnetic freezeout of electrons to occur in the $n^{-}$-GaAs. Sixteen periods are observed for $-0.6\mathrm{}\mathrm{V}<V_G<0\mathrm{}\mathrm{V}$. The phase and the voltage periodicity, 0.036 V, are independent of magnetic field. The mechanism appears to involve LO-phonon emission events by ballistic electrons. This is the first observation of sequential single-phonon emission observed in electron transport.

• Received 15 February 1984

DOI:https://doi.org/10.1103/PhysRevLett.52.2053