Effects of Thermal Annealing on In Situ Phosphorus-Doped Germanium $\hbox{n}^{+}/\hbox{p}$ Junction

In this letter, we investigate the electrical behavior of vacancy $V_{\rm Ge}$ defects in Ge at various thermal annealing conditions through electrochemical capacitance–voltage analysis. Then, the effects of the annealing process on Ge $\hbox{n}^{+}/\hbox{p}$ junction diodes were also studied with $J{-}V$, transmission electron microscopy, and secondary ion mass spectroscopy measurements in the aspects of point-defect healing and dopant diffusion/loss phenomena. The $V_{ \rm Ge}$ defects tend to heal by recombining with Ge interstitial atoms as the annealing process temperature increases. However, the diffusion/loss problems of P atoms in Ge become severe at above 500 $^{\circ}\hbox{C}$. Therefore, an optimal postfabrication annealing process at 600 $^{\circ}\hbox{C}$ is proposed in terms of point-defect healing and dopant diffusion/loss reduction.

I. Introduction

Recently, germanium (Ge) has been widely researched for technology beyond silicon (Si) complementary metal–oxide–semiconductor (CMOS) due to its higher carrier mobility and lower processing temperature than that of Si. However, one of the critical aspects that are currently plaguing the successful integration of Ge CMOS is its high drain–substrate junction leakage current caused by its relatively small energy band gap (0.66 eV) and, subsequently, a higher electron–hole pair generation rate. In addition, an ion implant a during CMOS process causes crystal damage, resulting in point defects [1] such as Ge vacancies and interstitial atoms that work as recombination sources. However, we note that normally exist as a form of -related complexes, such as vacancy–vacancy, vacancy–oxygen, and vacancy–phosphorus at room temperature [2]. These essentially act as trap states within the band gap that induces generation current , thereby increasing the total junction leakage current. In particular, in the Ge junction, acts as an acceptor-like trap [3] and subsequently compensates with n-type dopants, leading to low dopant activation and fast junction diffusion problems. In contrast to ion implantation, in situ doping technique [4] has the advantages of relatively low point-defect concentration and low dopant deactivation. However, the Ge junction formed even by in situ doping technique is degraded during the postfabrication process because of dopant diffusion. Although there are a few studies showing a decrease in by hydrogen (H) and fluorine (F) incorporation [5], [6], the effect of thermal annealing on the electrical behavior of was not clearly investigated. Therefore, the aim of this letter is to characterize the electrical role of at various annealing conditions through electrochemical capacitance–voltage (ECV) analysis and investigate the effects of postfabrication annealing on the Ge junctions in the aspects of point-defect healing and dopant diffusion/loss phenomena by current density–voltage –, transmission electron microscopy (TEM), and secondary ion mass spectroscopy (SIMS) analyses.