A search for materials suitable for implementation of 1.55 mu m 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.