This work is to present results of flash evaporation of PbTe directly over single crystals p-type Si substrates, in order to produce heterojunction infrared detectors (HIRD), working at 4.3μm IR wavelength. The evaporation was performed on modified JEOL vacuum equipment, model JEE4B(a), working with vacuum pressure around 10−5 torr, using diffusion pump. The HIRDs produced with this method presented the same detectivity (D*) values of HIRDs made with Hot Wall Epitaxial System (HWE)(b), in which PbTe epitaxial layers were grown directly over the same Si substrates, where an ionic pump reached about 10−7 torr as vacuum pressure. The best results, were obtained with PbTe layers grown with Molecular Beam Epitaxial (MBE) method(c) directly over Si substrates, where the vacuum pressure is around 10−9 torr, also using an ionic pump. The advantage of growing PbTe directly over Si wafers is that the HIRDs perform at room temperature. The detectivity values of HIRDs obtained with methods (a) and (b), were D*≈4,8 × 105 cm.Hz1/2 W−1 and with method (c), D* ≈ 6,7 × 106 cm.Hz1/2 W−1. Different technologies: (a) very low costs, (c) high technology; not very different results.