Exciton and Electron‐‐Hole Liquid Luminescence of Germanium in an Electric Field

Abstract

Xeasurements of the exciton and the electron-hole liquid (EHL) luminescence of optically pumped germanium are reported for the temperature range of 2.1 to 4.2 K in the presence of an electric field. Simultaneously with the luminescence the electrical conductivity behaviour is studied. At an electric field near 3.0V/cm the EHL luminescence sharply drops to zero. With increasing field the drop of the free-exciton luminescence is less sharp than that of the E H L luminescence and sets in as soon as the EHL luminescence vanishes. This field dependence together with the conductivity results can be explained by impact ionization of the free excitons. Apparently during this process the EHL acts as a buffer for the free-exciton system. Es werden Xessungen der Exziton-und der Elektron-Loch-Fliissigkeits-(EHL)-Lumineszenzvon optisch gepumptem Germanium im Temperaturbereich von 2,l bis 4,2 K im elektrischen Feld durchgefuhrt. Zusammen mit der Lumineszenz wird das Verhalten der elektrischen Leitfahigkeit untersucht. Bei elektrischen Feldern um 3,O V/cm fallt die EHL-Lumineszenz scharf auf null ab. Mit wachsendem Feld ist der Abfall der Lumineszenz freier Exzitonen weniger scharf als der der EHL-Lumineszenz und setzt ein, sobald die EHL-Lumineszenz verschwindet. Diese Feldabhangigkeit I l B t sich zusammen mit den Leitfiihigkeitsergebnissen durch die StoDionisation der freien Exzitonen erkllren. Offensichtlich wirkt die EHL im Verlauf dieses Prozesses als Puffer fur das System freier Exzitonen.

Exciton Impact Ionization and Electric Conductivity in Germanium at Low Temperature

“…Breakdown of the FE in Ge in microwave fields has been studied extensively by Keldysh, Manenkov, and coworkers [7 to 101. In addition to Ge, impact ionization of excitons has been investigated in GaP [ll], CdS 11121, and GaAs In the present paper we continue our earlier work on exciton and electron-hole liquid luminescence of Ge in an electric field [6]. In particular, we attempt to correlate our experimental data on the luminescence and the electric conduct,ivity with model calculations based on the rate equations.…”

“…The contact areas of the p-doped samples were prepared by depositing an A1 film of 2 pm thickness using the procedure described in [6]. The undoped samples were contacted in the following way.…”

“…The experiments reported in this paper were performed at the bath temperature of 4.2 K. All instrumentation was identical to that described in [ 6 ] , except that a Ge detector (North Coast model EO-817/VO-1) has been used for measuring the luminescence intensity at the output of the monochromator. An electronic discriminator served for eliminating spurious detector signals from pulsed external perturbations (high-energy particles).…”