NOVELTY - Forming a heterostructure semiconductor device (50) in a growth chamber with gas inlet, involves providing a silicon substrate (51) in the growth chamber on a substrate carrier; maintaining a constant substrate temperature (Ts) of the substrate at 350-500 degrees C during the deposition of a silicon germanium semiconductor layer (52); establishing a high-density, low-energy plasma in the growth chamber; directing Silane and Germane gas through the gas inlet into the growth chamber; performing an annealing step; and forming an active region (59) above the silicon germanium semiconductor layer.    USE - For forming heterostructure semiconductor device (claimed) useful in transistor, sensor, spectroscopy, quantum computers, and solar cell.    ADVANTAGE - The process suitable for large scale production; making silicon germanium layer has a high degree of relaxation i.e. 75% and thickness of 100-800 nm; is fast process; forming the semiconductor layer takes less than 5 (preferably 1-4) minutes; and larger thickness and composition can be more easily controlled.    DETAILED DESCRIPTION - Forming a heterostructure semiconductor device (50) in a growth chamber with gas inlet, involves providing a silicon substrate (51) in the growth chamber on a substrate carrier; maintaining a constant substrate temperature (Ts) of the substrate at 350-500 degrees C during the deposition of a Si1-xGex semiconductor layer (52) having a thickness of 100-800 nm; establishing a high-density, low-energy plasma in the growth chamber such that the substrate is being exposed to the plasma; directing Silane gas (SiH4) and Germane gas (GeH4) through the gas inlet into the growth chamber, the flow rates of the Silane gas and the Germane gas being adjusted in order to form the semiconductor layer by means of low-energy plasma enhanced chemical vapor deposition with a growth rate of 1-10 nm/s, the Si1-xGex semiconductor layer having a constant Germanium concentration (x) is 0-50% and a degree of relaxation of at least 75%; performing an annealing step with a temperature of 600-870 degrees C providing a surface roughness (rms) of Si1-xGex semiconductor layer having rms values of below 1.8 nm; forming an active region (59) above the Si1-xGex layer; and forming of the semiconductor layer. The growth chamber is a high-density, low-energy plasma enhanced chemical vapor deposition (LEPECVD) chamber. The substrate is silicon wafer or a Silicon-on-Insulator (SOI) substrate.    DESCRIPTION OF DRAWING(S) - The figure shows cross-sectional view of a silicon germanium heterostructure semiconductor device.    Heterostructure semiconductor device (50)    Substrate (51)    Semiconductor layer (52)    Spacer (55)    Active region (59)