electrons and holes in gaas the results were then translated using the 3 2 power rule to obtain the equivalent bv ceo data for alas preliminary experimentation correlates well with the program calculations it is readily evident from the first three data points plotted in fig2 which represent the performance of a standard one layer collector structure as shown in table i that there is an almost perfect inverse relationship between j max and bv ceo for these devices by contrast data points 4 5 and 6 which represent the performance of devices constructed according to the first preferred embodiment of the present invention as shown in table i illustrate that j max can substantially be increased independent of any effect on bv ceo by simply changing the thickness w c1 and the doping concentration n c1 of the first collector layer 12 additionally a sensitivity analysis has been performed which shows that for hbts designed for x band applications in which the collector thickness w c2 is limited to 1 u03bcm the unintentionally doped second collector layer 14 can have a doping concentration n c2 as high as 1 u00d7 10 16 atoms cm 3 donor or acceptor before a sudden drop of bv ceo takes place since growth techniques such as molecular beam epitaxy mbe and metal organic chemical vapor deposition mocvd can reproducibly grow unintentionally doped layers at doping concentrations below 1 u00d7 10 15 atoms cm 3 and often achieving a concentration of 1 u00d7.