在本文中,我們開發的真空能階系統,E_0方法,去解決模擬2-D異質結構的半導體元件邊界條件上的問題。在過去,我們的程式是使用本質費米能階,E_fi,以其來計算載子濃度與電位電場情形。然而,E_fi這個方法在2D異質接面上有模擬的問題。所以發展了E_0系統去計算邊界條件並解決問題。而在之後的章節,我們去驗證E_0方法製作出的模型是否可行,藉由pN接面元件與理論討論。並探討陡變接面與漸變接面在模擬上的問題。最後,我們使用的方法E_0,做出HBT並模擬,且著重在能隙寬度對於電壓電流特性的比較。;In this thesis, we develop vacuum level system, E_0 method, for numerical 2-D heterojunction device simulation. In the past, our program use intrinsic Fermi level, E_fi, to calculate carrier concentration and potential. However, the E_fi modeling has problem in heterojunction. The E_0 method has been verified by a pN heterojunction. And discuss problems of simulation happened on abrupt. Finally, we use the E_0 method to compare HBT with BJT to discuss the electrical characteristics.