本文探討在製程研發結果具有外溢效果，並允許研發量為角解的情況下，雙佔廠商最適的決策行為。過去在具有研發外溢的雙佔廠商製程研發的研究中，對廠商的研發效率與成本結構均有範圍上的限制。廠商在決策時並不能控制研發效率與成本結構這一類外生給定的變數，故本研究放寬對於外生變數的範圍限制，詳細討論在各種情況下，廠商如何進行決策。 在考慮到研發外溢的情況下，既有文獻因為設定廠商條件完全對稱，所求出的兩家廠商最適研發量相同，且為唯一的內部解。本文允許廠商條件不對稱，依照不同的成本組合，分區討論廠商的研發決策與市場形態。在能夠處理角解的模型中，廠商的決策行為與市場形態依據外溢程度的大小不同會產生結構性的變化。在外溢程度發生變化的時候，即使廠商成本結構並未變化，但是最終的決策以及市場情況也會有所不同，市場可能由廠商獨佔轉為雙佔情形。此外，本文發現，雖然在外溢程度較大時可能存在多個均衡，在兩家廠商的行為可以達成一致時，廠商偏好能給自身帶來更多利潤的高度研發均衡。在福利分析中，廠商自身的研發效率大小與外溢程度都影響廠商在研發階段合作與不合作時的福利排序。研發階段不合作時，廠商若已經達到了完全研發的水準，合作就會導致過度研發。在廠商條件對稱時，外溢程度的變化亦會對廠商利潤產生影響。;This thesis considers process R&D with spillover effect in a Cournot model and allows the existence of corner solution in results. Previous studies restrict the ranges of R&D efficiency and marginal cost. Actually, these parameters are often seen as exogenous and can not be controlled by firms. We discuss how duopoly firms decide investment and production strategies without such restrictions. Previous studies often consider the symmetric case, such way leads to the interior and identical results. Allowing the duopoly firms be asymmetric, we explore their best-response functions under various combinations of R&D efficiency and marginal cost parameters. Firms′ decisions and market situation are totally different when the level of spillover effect changes, even if the R&D efficiency and marginal cost remain unchanged. For instance, the monopoly market will transform to duopoly situation. Furthermore, there are multiple equilibrium when the spillover effect is large. Firms prefer the equilibrium with higher R&D investment when it leads more profit to both of them. By comparing the R&D investments between cooperation and noncooperation in R&D stage, we find R&D efficiency and the level of spillover effect will affect the welfare order of them. If firms have achieved completely R&D level when they are noncooperation in R&D stage, switching to cooperation leads to excessive R&D. The change of spillover effect also affect firms′ profit when they are symmetric.
