TUNNELING FROM QUASI 2D ELECTRONIC STATES INTO CONTINUUM- AND BOUND STATES IN GaAs/GaAlAs-HETEROSTRUCTURES

Osci l l a to ry s t r u c t u r e i s observed i n forward biased dI/dV and d21/dV2 curves of conventional GaAs/GaAlAs high e lec t ron mobil i ty t r a n s i s t o r samples a t l i q u i d helium temperature using modulation techniques. These osc i l l a t i o n s can be explained by Fowler-Nordheim tunneling. From t h e pos i t ion of t h e o s c i l l a t i o n s t h e conduction band d i scont inu i ty is determined a s a funct ion of the aluminum concentration X. For samples having an aluninun concentration between 0.3 and 0.4 a value of AE /AE = 0.61 i s found. Further t h e depth of t h e deep donor l e v e l s i n t h e G a A l f I s w%s determined t o be 130 meV below t h e conduction band. I n most recent experiments tunneling between subbands i n t h e GaAs and GaAlAs i s observed.