A short wavelength red light 640 nm high power laser diode has been designed and fabricated. AlGaInP epitaxial layers of the laser diodes are grown by metal organic chemical vapor deposition. The cladding layers are AlInP with low refractive index. The active layer is tensile strained GaInP/AlGaInP quantum well. The photoluminescence spectrum of the active layer shows two splitting peaks locate at 627 nm and 616 nm, which correspond to the transitions from electrons to light holes and heavy holes, respectively. Zn atoms are selectively diffused into the window region, leading to the mixing of the quantum well. The wavelength is blue-shifted by 43 nm. The catastrophic optical damage (COD) occurs for the laser diode without window structure at 1.9 A, corresponding to the power of 1.4 W. The device with window structure has no COD phenomenon. The output power is limited by the thermal rollover with the maximum of 2.3 W. At room temperature, the wavelength of the laser diode is 639 nm at 1 A while 640 nm at 1.5 A. The horizontal divergence angle of the device is 6° and the vertical divergence angle is 41°.