Using numerical simulation, the search for designs of asymmetric barrier layers (ABLs) in a laser diode with a GaAs waveguide emitting at a wavelength of λ = 980 nm is carried out. A pair of ABLs ...adjoining the active region on both sides blocks undesired charge-carrier flows and suppresses parasitic spontaneous recombination in the waveguide layers. Optimal designs of ABLs based on AlGaAsSb and GaInP for blocking electrons and holes, respectively, are proposed, which make it possible to reduce the parasitic recombination current down to less than 1% of the initial value. To suppress electron transport, an alternative structure based on three identical AlInAs barriers is also proposed. The GaAsP spacer layers separating these barriers from each other have different thicknesses. Due to this, the set of quasibound (resonant) states is formed in each spacer layer that is different from the set of states of the neighboring spacer layer. As a result, the resonant tunneling channels are blocked, and the parasitic electron flow is reduced by several tens of times in comparison with the case of spacers of identical thickness.
In a laser with asymmetric barrier layers (ABLs) two thin barrier layers adjacent to the active region on both sides are intended to prevent bipolar population of the waveguide layers, hence, to ...suppress parasitic recombination in them. A theoretical model of a laser with ABLs, based on rate equations which acknowledge undesirable carrier leakage inevitable in lasers of this type implemented in practice, is proposed. Solutions to equations are obtained for the steady-state case. By the example of an InGaAs/GaAs quantum-well laser (lasing wavelength λ = 980 nm), the effect of leakages through ABLs on the device characteristics is studied. The parasitic-flux suppression ratios
C
of ABLs which are required to prevent the adverse effect of waveguide recombination are estimated. In the case at hand, the effect of ABLs becomes appreciable at suppression ratios of
C
≥ 10
2
. To suppress 90% of the parasitic current,
C
should be 2.3 × 10
4
. The effect of ABLs on useful carrier fluxes arriving at the active region is also studied.
A self-consistent model for calculating the threshold and high-power characteristics of semiconductor quantum well lasers with asymmetric barrier layers is developed. The model, which is based on a ...system of rate equations, uses the universal condition of global charge neutrality in the laser structure. The electron and hole concentrations in the waveguide region and in the quantum well (QW) and the concentration of photons of stimulated emission are calculated. The local neutrality in the QW is shown to be strongly violated, especially at high injection currents. The violation of neutrality in a QW makes the electron and hole concentrations there dependent on the injection current under lasing conditions: in the structures under consideration, the electron concentration in the QW decreases while the hole concentration increases with increasing injection current. In the case of the ideal functioning of asymmetric barrier layers, when electron–hole recombination in the waveguide region is completely suppressed, the violation of neutrality in the QW has almost no effect on the dependence of the output optical power on the injection current: the quantum efficiency is close to unity and the light–current characteristic is linear. Nevertheless, the violation of neutrality in the QW causes weakening of the temperature dependence of the threshold current and, hence, an increase in the characteristic temperature
T
0
of the laser.
A search for materials suitable for implementation of 1.55 µm Al-free diode lasers based on InP with asymmetric barrier (AB) layers is conducted. It is shown that a very high (over 10
6
) suppression ...ratio of the parasitic electron flux can be achieved using common III–V alloys for the ABs. Hence placing such ABs in the immediate vicinity of the active region should completely suppress the parasitic recombination in the waveguide. Several optimal AB designs are proposed that are based on one of the following alloys: Al-free GaInPSb, ternary AlInAs, or quaternary AlGaInAs with a low Al-content. As an important and beneficial byproduct of utilization of such ABs, an improvement of majority carrier capture into the active region occurs.
We study the possibility of realization of the asymmetric barrier layers (ABL) concept in an 808-nm Al-free GaInAsP/InGaP/GaAs semiconductor laser. Two ABLs on both sides of the active region are ...aimed to suppress the parasitic recombination in the optical confinement layers. It is shown that such ABL-laser can be made fully Al-free having high suppression ratios for parasitic charge carrier flows (60 and 207 times for electrons and holes, respectively, as compared to a conventional SCH heterostructure).
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