The diffusion of Zn through MOCVD-fabricated InP and InGaAsP layers, and the corresponding Zn doping profile at the heterojunction interface were studied (figures 11 and 12). It was found that the Zn doping profile had a specific discontinuity at the heterojunction in InGaAsP/InP heterostructures. Using secondary ionization mass spectrometry and Boltzmann–Matano analysis for various composition ratios (x) of (1−x)InP–xInGaAs epitaxial layers grown onto Zn-doped InP substrates, it was found that the Zn diffusion coefficients were proportional to the square of the concentration in the InP and InGaAsP layers. The Zn diffusion coefficient depended strongly upon the component ratio (x) for the (1−x)InP–xInGaAs layer. It was concluded that this diffusion property was based upon the higher stability of the substitutional Zn content in the InGaAs layer compared to that in the InP layer. The dependence of the Zn diffusion coefficient on Zn concentration in the InGaAsP/InP layers was explained on the basis of the main diffusion source being Zn at interstitial sites. Thermal equilibrium between Zn-interstitial and Zn-substitutional processes explained the Zn diffusion properties. Marked Zn concentrations at InGaAsP/InP heterojunctions were referred to as pile-ups, and were attributed to the differing properties of InP and InGaAs. With different ratios (x) of InP/InGaAsP layer growth, pre-control of the Zn concentration and strict limitations on the growth conditions before diffusion were indispensable.

Zn Diffusion Behavior at the InGaAsP/InP Hetero-Interface Grown using MOCVD. K.Kadoiwa, K.Ono, Y.Ohkura: Journal of Crystal Growth, 2006, 297[1], 44-51