Effect of As4 overpressure on initial growth of gallium arsenide on silicon by molecular beam epitaxy

Abstract

We have demonstrated great improvement in the smoothness and defect density of GaAs films on Si by lowering the arsenic overpressure during growth of the initial layer (the first 500 Å) of GaAs. We have studied the morphology and defect density of GaAs on Si films in which the initial layers were grown under either low As₄ overpressure (7As₄:1Ga, beam equivalent pressure) or high As₄ overpressure (15As₄:1Ga) conditions, with a constant gallium flux. In the early stages of growth there is a significant change in island morphology depending on the As₄ overpressure. There is dramatic improvement of surface smoothness and crystal quality with reduced arsenic overpressure for 500‐Å‐thick layers both immediately after growth at 350 °C and after heating to 580 °C. Diodes fabricated in 3.5‐μm‐thick films grown on initial layers that were grown under low arsenic overpressure have a very sharp reverse breakdown at voltages as high as 45 V, whereas diodes fabricated in films grown on initial layers that were grown under high arsenic overpressure have a soft reverse breakdown at about 5 V. This demonstrates a significant reduction in the density of electrically active defects in the thick GaAs films with decreasing arsenic overpressure conditions during growth of the initial 500 Å of GaAs on Si. The improvement in film quality for low As₄ overpressures is discussed in terms of the observed changes in island morphology.