The concept of the transport energy (TE) has proven to be one of the most powerful theoretical approaches to describe charge transport in organic semiconductors. In the recent paper L. Li, G. Meller, and H. Kosina [Appl. Phys. Lett. 92, 013307 (2008)] have studied the effect of the partially filled localized states on the position of the TE level. We show that the position of the TE is essentially different to the one suggested by L. Li, G. Meller, and H. Kosina [Appl. Phys. Lett. 92, 013307 (2008)] We further modify the standard TE approach taking into account the percolation nature of the transport path. Our calculations show that the TE becomes dependent on the concentration of charge carriers n at much higher n values than those, at which the carrier mobility already strongly depends on n. Hence the calculations of the concentration-dependent carrier mobility cannot be performed within the approach, in which only the concentration dependence of the TE is taken into account.
Electrical injection lasers emitting in the 1.3 μm wavelength regime based on (GaIn)As/Ga(AsSb)/(GaIn)As type-II double “W”-quantum well heterostructures grown on GaAs substrate are demonstrated. The structure is designed by applying a fully microscopic theory and fabricated using metal organic vapor phase epitaxy. Temperature-dependent electroluminescence measurements as well as broad-area edge-emitting laser studies are carried out in order to characterize the resulting devices. Laser emission based on the fundamental type-II transition is demonstrated for a 975 μm long laser bar in the temperature range between 10 °C and 100 °C. The device exhibits a differential efficiency of 41 % and a threshold current density of 1.0 kA/cm2 at room temperature. Temperature-dependent laser studies reveal characteristic temperatures of T0 = (132 ± 3) K over the whole temperature range and T1 = (159 ± 13) K between 10 °C and 70 °C and T1 = (40 ± 1) K between 80 °C and 100 °C.
Highly efficient interface-dominated electrical injection lasers in the near-infrared regime based on the type-II band alignment in (GaIn)As/Ga(AsSb)/(GaIn)As single 'W'-quantum wells are realised. The structure is designed by applying a fully microscopic theory, grown by metal organic vapour phase epitaxy, and characterised using electroluminescence measurements and broad-area laser studies. A characteristic blue shift of 93 meV/(kA/cm 2) with increasing charge carrier density is observed and compared with theoretical investigations. Low threshold current densities of 0.4 kA/cm 2 , high differential efficiencies of 66%, optical output powers of 1.4 W per facet, and internal losses of only 1.9 cm −1 are observed at a wavelength of 1164 nm for a cavity length of 930 µm. For a cavity length of 2070 µm, the threshold current density is reduced to 0.1 kA/cm 2. No indication for type-I related transitions for current densities up to 4.6 kA/cm 2 is observed.
A series of (Ga,In)As/GaAs/Ga(As,Sb) multi-quantum well heterostructures is analyzed using temperatureand power-dependent photoluminescence (PL) spectroscopy. Pronounced PL variations with sample temperature are observed and analyzed using microscopic many-body theory and band structure calculations based on the k·p method. This theory-experiment comparison reveals an unusual, temperature dependent variation of the band alignment between the (Ga,In)As and Ga(As,Sb) quantum wells.
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