Accurate in-situ lattice matching by reflection high energy electron diffraction

A multiple quantum well modulator fabricated by the steps of:

• (a) providing a substrate of a first semiconductor material;
• (b) initiating growth of a film composed of a second semiconductor material on the substrate;
• (c) monitoring intensity I of reflection high energy electron diffraction spot of the film and the substrate over multiple waveform cycles;
• (d) determining a maximum intensity I.sup.+ and a minimum intensity I.sup.- of each waveform cycle;
• (e) determining an intensity drop .DELTA.I from initial reflectivity, measured prior to initiating growth, to minimum reflectivity measured after starting growth;
• (f) calculating a normalized figure of merit FM for each said waveform cycle wherein
• FM=(.SIGMA.(I+-I-) )/.DELTA.I
• for each said waveform cycle;
• (g) adjusting cell temperature to maximize FM and optimize lattice matching:
• and
• (h) repeating steps (c)-(g) to form a plurality of alternating films of said first and second semiconductor materials, said alternating films forming a multiple quantum well region of at least 4 .mu.m thick and having a lattice mismatch of less than two parts in 10.sup.4, and said multiple quantum well modulator exhibiting a contrast ratio of at least 8:1 when operated in a reflectivity mode with a single light beam of a wavelength in the range of about 1.5 to 1.6 .mu.m.