In high-speed fiber-optic communication systems， modulation bandwidth is a critical performance indicator for characterizing data transmission rates. Owing to the short carrier recombination lifetime in their active regions， transistor lasers have become a major research focus. Nevertheless， their direct modulation bandwidth is typically limited by carrier leakage， which significantly degrades device performance. In this work， a deep-ridge waveguide transistor laser with an InAlAs carrier blocking layer is proposed and numerically studied. The proposed structure effectively improves carrier injection efficiency and thus achieves bandwidth enhancement in transistor lasers.The physical models primarily employed in this work include the classical drift-diffusion model for carrier transport， the thermionic emission model for heterojunction transport， and the effective index method for the calculation of transverse optical modes. The optical gain is computed using the 4×4 k·p band theory with the valence band mixing effect fully considered. Numerical simulations are carried out to comparatively analyze the current gain， current distribution， and bias-dependent small-signal frequency response of both the conventional deep-ridge waveguide transistor laser and the device with embedded InAlAs layers. Furthermore， the influences of key structural parameters， including the thickness and doping concentration of the InAlAs layers， on the -3 dB modulation bandwidth of the proposed device are systematically investigated.For the conventional deep-ridge waveguide transistor laser， a current gain of up to 4.3 is achieved at a base current of 8 mA， indicating excellent current amplification performance. At a bias current of 3 times the threshold current， the –3 dB small-signal modulation bandwidth under CE mode is approximately 3 GHz. As the base bias current further increases， the improvement in bandwidth becomes limited； the –3 dB bandwidth reaches 12 GHz at an emitter bias current of 3 times the threshold current. For comparison， the deep-ridge transistor laser with InAlAs layers is investigated under identical conditions. At a bias current of 3 times the threshold current， the –3 dB small-signal modulation bandwidth under CE mode is extended to 8 GHz. At an emitter bias current of 3 times the threshold current， the –3 dB bandwidth reaches 18 GHz， and it can be further enhanced to 38 GHz at 12 times the threshold current， demonstrating a significant improvement in the modulation bandwidth.Furthermore， the effects of InAlAs layer thickness and doping concentration on the –3 dB bandwidth are studied for the proposed structure. The results reveal that under CB mode， the device achieves a modulation bandwidth of 38 GHz when the doping concentration and thickness of the InAlAs layer are set to 9×10¹⁸ cm⁻³ and 100 nm， respectively， at a bias current of 12 times the threshold current.Simulation results show that the introduction of the InAlAs layer can confine the optical field within the quantum-well active region， enhancing the light-carrier interaction in the active area. This in turn increases the relaxation oscillation frequency and improves the high-frequency modulation capability of the device. Meanwhile， increasing the doping concentration of the InAlAs layer optimizes carrier transport characteristics， improves the effective injection efficiency from the base region into the active region， and reduces the charge storage time. As a result， the device can maintain a relatively stable carrier concentration distribution at high frequencies， further refining the modulation response and extending the modulation bandwidth.