Abstract

The photoassisted OMVPE growth technique is important for the fabrication of blue/green laser diodes based on Cd x Zn 1-x Se quantum wells. Low temperature growth with photoassistance is key to the fabrication of these devices, however, the compositional control of Cd x Zn 1-x Se becomes increasingly difficult as the growth temperature is reduced. We have studied the compositional control of Cd x Zn 1-x Se using the sources DMCd, DMZn, and DMSe, with irradiation from a Hg arc lamp. We studied the dependence of the composition on the growth temperature, irradiation intensity, and source mass flows. The composition x increases with increasing temperature and decreases with increasing irradiation intensity. The solid-phase composition is a non-linear function of the gas-phase composition X. The slope of this characteristic, dx/dX, should be minimized for good compositional control. At 475°C without photoassistance, dx/dX is 1.75 near a composition of 20%, as determined from the data of Parbrook et al. Decreasing the temperature increases dx/dX. At 370°C with 12 mW/cm 2 , dx/dX 13 and at 350°C with 58 mW/cm 2 dx/dX 60. We have investigated this behavior at 370°C with 12 mW/cm 2 irradiation by studying both the composition and the growth rate as a function of the gas-phase composition. The growth rate is non-monotonic, and is minimum for a gas-phase composition of ∼ 0.20. The behavior is quite complex, and is not fully understood at the present time. Nonetheless, our results indicate that the Cd-bearing precursor is adsorbed much more strongly than the Zn-bearing precursor. In addition to this, the introduction of the DMCd strongly inhibits the growth of ZnSe. We have achieved sufficiently good compositional control at 370°C and 12 mW/cm 2 to grow ZnSe/Cd x Zn 1-x Se/ZnSe multiple quantum well structures. More work is necessary in order to clarify the roles of irradiation intensity and VI/II ratio so that good compositional control can be achieved at lower growth temperatures.

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