Field injection of low-energy electrons into the ZnSe/CdSe/ZnSe heterostructure with the use of an ultra-high-vacuum tunneling microscope

Abstract

In lasers with electron beam pumping, the semi conductor crystal transforms the energy of the acceler ated electron beam into the laser emission with a wavelength corresponding to the band gap of the used semiconductor. Pumping with the fast electron beam is a universal method of lasing in semiconductor mate rials with any band gap E g and any starting resistivity. Such lasers make it possible to generate optical pulses with a power of several tens of megawatts in a broad spectral range from the mid IR to near UV range.The main advantage of the lasers with electron beam pumping is in the absence of necessity of doping the used semiconductor materials. Elimination of requirements to p doping is especially essential for wide band gap semiconductor structures formed based on Group II-VI and III-V elements. Electron energy in electron beam pumping is relatively high, namely, 5-100 keV [1,2]. The necessity of using such energies is associated with low efficiency of penetra tion of the electron beam into the solid. Upon varying the energy of electrons from 10 to 200 keV, their effec tive penetration depth varies from 1 to 60 μm [3]. The active region of the laser with transverse electron beam pumping is usually arranged at a distance of several micrometers from the surface. It was shown as a result of numerous experimental investigations of impact ionization [4, 5] that average energy 〈E〉 necessary for the formation of one pair of carriers under the effect of the primary electron is determined only by the band gap of semiconductor 〈E〉 ≈ 3E g . Therefore, electrons with an energy of several tens and hundreds of kilo electronvolts possess the deliberately excessive energy.The use of high energy electrons causes the problems associated with carrier thermalization to equilibrium temperatures. This leads to nonuniform heating of the crystal lattice, appearance of local mechanical stresses, and overheating of the quasi equilibrium electron-hole plasma (which appears during pair Coulomb collisions) in the active region of the laser [3]. A decrease in the excessive energy of the electron beam eliminates the problems associated with the sub sequent thermalization and, as a consequence, leads to a decrease in the threshold current density. In recent time, a stable tendency to decreasing the pump elec tron beam energy is observed. The use of the miniature field electron source in [6] made it possible to fabricate compact lasers operating at beam energies of 7-10 keV in the near IR range at 90-300 K.In this work, we evaluated the efficiency of the use of the low voltage field electron emission for electron beam pumping. As the electron source, the metal probe of an LS SPM ultra high vacuum probe micro scope (OMICRON) is used. The probe of the ultra high vacuum scanning tunneling microscope (STM) is moved closer to the heterostructure under study to a distance of several nanometers. With the negative bias voltage of several volts supplied to the metal probe, field electron emission from the metal surface appears under the effect of...