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Teke, Ahmet (Balikesir Author), We demonstrate the operation of a novel tunable wavelength surface emitting device. The device is based on a p-GaAs and n-Ga1-xAlxAs heterojunction containing an inversion layer on the p-side, and GaAs quantum wells on the n-side, and is referred to as HELLISH-II (hot-electron light emitting and lasing in semiconductor heterojunction). The device utilizes hot-electron longitudinal transport and, therefore, light emission is independent of the polarity of the applied voltage. Because of this symmetric property, the device can perform light logic functions. The wavelength of the emitted tight can be tuned with the applied bias from GaAs band-to-band transition in the inversion layer to e1-hh1 transition in the quantum wells. The operation of the device requires only two diffused in point contacts. Therefore, a two-dimensional array of surface emitters can be fabricated very cheaply and easily. Theoretical modelling of the device operation is carried out and compared with the experimental results. An optimized structure for high-efficiency device operation, as based on our model calculations, is also proposed.

The influence of a non-equilibrium population of LO phonons (hot phonons) on hot-electron energy and momentum relaxation in modulation-doped GaAs quantum wells are studied both experimentally and theoretically. The experimental results on high-field parallel transport indicate strongly that: (i) non-equilibrium phonons in GaAs quantum wells, contrary to the assumptions made in the conventional theories, are non-drifting; (ii) therefore, the production of hot phonons not only reduces the energy relaxation rate but also enhances the momentum relaxation rate; (iii) the enhancement of the momentum relaxation at high fields inhibits negative differential conductivity via real space transfer or intervalley transfer; (iv) the enhancement of the momentum relaxation rate also reduces the drift velocity at high fields, which is detrimental to the speed of the hot electron devices; (v) hot phonon effects increases with increasing 3D carrier concentration. The results are compared with a comprehensive theoretical model involving non-drifting hot phonons and scattering from remote impurities and interface roughness. The agreement between the theory and the experiments is excellent.

Experimental results on high-field parallel transport in selectively doped GaAs/GaAlAs HEMT structures are reported. The results indicate that in lightly doped material (n=3.92*1011 cm-2), the effective rate of electron energy relaxation (EER) by LO phonons, is ( tau e) approximately 213 fs. This is about a factor of two faster than that in more heavily doped material (n=8.85*1011 cm-2). The high-field drift velocity saturates at nu ds=1.2*107 cm s-1 in the former and at nu ds=8*106 cm s-1 in the latter. The experimental results are compared with a model of high-field transport involving non-drifting hot phonon effects.

Experimental data concerning high-field parallel transport in GaAs/GaAlAs quantum well structures are reported. The results strongly suggest that (i) in modulation doped GaAs quantum wells the non-equilibrium LO phonons (hot phonons) are non-drifting, and (ii) in samples with similar 2D electron densities hot phonon effects increase with reduced dimensionality, and hence with increasing 3D electron concentration. Both observations are in excellent agreement with a recent model of high-field transport involving hot phonons.