ingaas and inp ingaasp the thickness of the barrier layer preferably lies within the range of 100 nm to 500 nm the preferred algainas barrier material has a composition that is preferably lattice matched to inp although it can be slightly strained as long as the thickness of a strained layer does not exceed the pseudomorphic limit beyond which dislocations are generated preferably the algainas barrier material has an al content between an alinas composition and an algainas composition providing a bandgap wavelength of u03bb g 1 3 u03bcm the bandgap energy of al x ga y in 1 x y as that is lattice matched to inp is given by and the bandgap wavelength is given by equ1 the barrier layer may additionally contain other constituents to provide more complete bandgap and strain engineering in particular some phosphorus may be included a first embodiment of the invention is shown in cross section in fig3 on an n type inp substrate 30 are epitaxially deposited an n type inp buffer layer 32 having a thickness of 0 5 to 1 0 u03bcm over which is epitaxially deposited an algainas barrier layer 34 having a photoluminescent bandgap of u03bb g 0 95 u03bcm its thickness is the range of 0 1 to 0 5 u03bcm in general in a diode structure the layers on opposite sides of the active region are fairly heavily doped to opposite conductivity types however the doping is required only if the layer is relatively thick if their thickness is 0 1 u03bcm or less undoped or partially doped layers still provide the required.