A mass transport process for use in the manufacture of semiconductor devices, particularly but not exclusively low threshold semiconductor lasers in the InP/InGaAsP system, involves the arrangement of a cover wafer (18) of the material to be grown adjacent to a semiconductor wafer (15) on which the material is to be grown, their disposition together with a crystalline alkali halide (20) in a crucible (16), and heating the crucible, which is almost but not completely sealed, in a hydrogen stream.
For the manufacture of InP/InGaAsP lasers and the growth of InP, the alkali halide may comprise KI, Rbl or Csl and a controlled amount of In metal (21) may be optionally contained in the crucible (16) to control the balance between growth of InP for defining the laser active region and erosion of InP from other areas of the wafer. Growth is achieved at temperatures comparable with liquid phase epitaxy processing temperatures.