Conclusions: We Have Reported Cw Operation of 1-5 Fim Buried Ridge Structure Lasers Grown Entirely by Lp-mocvd. These Results from a Structure Which Is Not yet Optimised

As device dimensions decrease, the physics of nonequilibrium transport becomes increasingly important. However, the study of nonequilibrium transport has suffered from one serious disadvantage, namely that the distribution function of electrons has not been determined directly. We demonstrate a method for obtaining the distribution function using a planar doped barrier as a 'hot electron spectrometer'. We measure the distribution function of electrons that have traversed 1600 A of H-type (1 x 10 cm") GaAs after being injected from a potential of 0-2 eV. Our results demonstrate that the electron distribution peaks at very low energies and is not Maxwellian, which would be expected if the electrons thermalised while transiting the base. Neither is the distribution a displaced Maxwellian, which would be expected if little scattering occurred. Our measurements are based on the planar doped barrier transistor (PDBT), which has received attention in recent years' because of its possible application as a high-frequency microwave amplifier. Unfortunately, the transistor showed poor emitter grounded characteristics, attributed to the scattering of hot electrons by coupled plasmon-optical phonon modes in the base. With a small modification, the transistor structure shows considerable promise for the study of nonequilibrium effects which are important for the understanding of future devices characterised by hot-electron effects. The PDBT was formed by the MBE growth of two back-toback planar doped barriers (PDBs) on a <100> semi-insulating GaAs substrate. The PDB is a bulk triangular barrier that was formed by placing a thin p (Be-doped) layer in an undoped region bounded on each side by n (Si-doped) layers. The device structure used to determine the nonequilibrium distribution function of electrons differs from previous PDBTs in that the collector barrier (d)bc) was at a higher energy than the emitter barrier ((pbe). The GaAs semiconductor layers comprising the device are shown in Fig. 1 and the resulting conduction bandedge is shown in Fig. 2. When the emitter junction is forward-biased with 0-2 V it injects a displaced Maxwellian distribution with an excess energy above the Fermi energy of 0-2 eV. The injected electron distribution is modified by inelastic scattering events while transiting the n (1 x 10 cm") 1600 A base region. The device is designed such that electrons are injected at a relatively low mean energy (0-2 eV) so that intervalley scattering will not greatly influence the results. With the base and collector grounded, no electrons are collected as none have sufficient energy to surmount the base/