Two different quantum well heterostructure wafers are used to fabricate buried‐heterostructure AlxGa1-xAs‐GaAs quantum well lasers using Si‐induced layer disordering (via Si diffusion). In contrast to the first wafer (QWH1), the second quantum well wafer (QWH2) utilizes Zn instead of Mg as the p‐type dopant in the top AlxGa1-xAs confining layer and yields, because of concentration mismatch in acceptor and donor doping in the confining layers (nZn≫nSe), inferior laser diodes owing to Zn diffusion from the p‐type to the n‐type confining layer during high temperature processing (850 °C Si diffusion). The first quantum well heterostructure, however, employs a lower concentration Mg doping for its p‐type confining layer (nMg≪nSe) and yields high performance devices when used with the Si‐induced layer‐disordering process. For QWH1 the p‐n junction and injection is not displaced (as for QWH2) from the QW active region during Si‐induced layer disordering (850 °C annealing). A fabrication process is presented in which quantum well laser diodes are built with active regions as narrow in width as 0.6 μm, cw room‐temperature laser threshold currents as low as 3 mA, and pulsed current thresholds as low as 1.5 mA.