COMPARATIVE-STUDY OF MOLECULAR-BEAM INJECTION SYSTEMS FOR GAS-SOURCE MOLECULAR-BEAM EPITAXY

We compared the molecular beam characteristics of possible injection s ystems for gas source MBE (GSMBE). Key properties such as angular dist ribution of the emerging molecular beam and its intensity have been st udied in terms of homogeneity and overall growth rate. For example, ef fusion sources have a predictable and well defined profile with simult aneously low throughput. The use of long capillaries (diameter almost- equal-to 3 mm, length almost-equal-to 200 mm) at somewhat higher press ures offers greater simplicity and high flow rates. However, Monte Car lo simulations performed on the latter system show that it produces a beam profile which strongly depends on the operating conditions. This study shows that there is no ideal molecular beam source for GSMBE; th e choice will be determined by the actual requirements given by growth rate, uniformity and efficiency for the deposition of the respective material system.