We employ constant-Fermi-level ab initio molecular dynamics to investigate defects at the InGaAs/oxide interface upon inversion. We adopt a substoichiometric amorphous model for modelling the structure at the interface and investigate the formation of defect structures upon setting the Fermi-level above the conduction band minimum. The defect formation is detected through both an analysis of the atomic structure and a Wannier-decomposition of the electronic structure. This computer driven approach is able to retrieve In and Ga lone-pair defects and As-As dimer/dangling bond defects, in agreement with previous studies based on physical intuition. In addition, the present simulation reveals hitherto unidentified defect structures consisting of metallic In-In, In-Ga, and Ga-Ga bonds. The defect charge transition levels of such metallic bonds in Al2O3 are then determined through a hybrid functional scheme and found to be consistent with the defect density measured at InGaAs/Al2O3 interfaces. Hence, we conclude that both In and Ga lone pairs dangling bonds and metallic In-In bonds are valid candidate defects for charge trapping at InGaAs/oxide interfaces upon charge carier inversion. This study demonstrates the effectiveness of constant-Fermi-level ab initio molecular dynamics in revealing and identifying defects at InGaAs/oxide interfaces.