Investigation of Heterojunction Bipolar Transistors Using Metallic P-Type Base Layer

To realize ultra-high speed heterojManagement bipolar transistors （HBTs）， a "metallic" base layer with extremely low base resistance is necessary。在本工作中，碳掺杂金属p型GaAs层生长由金属有机分子束epitaxy （MOMBE）使用三甲基伽利um（TMG）和固体砷。A hole concentration of 1.5 x10 ^<21>cm^&lt;-3&gt; a resistivity of 1.9 x10 ^&lt;-4&gt; OMEGAcm已被发现，其中是GaAs报告如此之高的hole concentration。在更远的地方，碳被发现比其他P型剂量差得多，例如beryllium和锌c，甚至在极高的剂量水平。因此，碳是HBT应用的首选剂量。However，在高剂量水平上，通过增加载体集中，在重碳掺杂p-GaAs和中等剂量GaAs之间创造了一种晶格不匹配。为了补偿这种晶格不匹配，一个小的印度化合物数量增加到生长InGaAs。A hole concentration of 2.6 x10 ^<20>cm^\-3&gt; was obtained for InGaAs （In-5%） lattice matched to GaAs substrate。它还发现了一种与载体集中的碳掺杂的GaAs脱氮的带隙由于这个收缩是一个大的200兆伏，形成了5x 10 ^<20>cm^&lt;-3&gt;的孔集中，一个假HBT已经提出，因此，在发射层中使用了GaAs。在假HBTs中，因为在基础上重碳掺杂的GaAs中的带隙收缩，具有高发射剂注入效率和出色的高频率性能是预期的，作为传统HBTs。A pseudo-HBT with 100 nm thick base （p= 1 x10 ^<20>cm^\-3\） was fabricated and a DC current gain of 1.7 was obtained。

To realize ultra-high speed heterojunction bipolar transistors (HBTs), a "metallic" base layer with extremely low base resistance is necessary. In this work, carbon doped metallic p-type GaAs layers were grown by metalorganic molecular beam epitaxy (MOMBE) using trimethylgallium (TMG) and solid arsenic. A hole concentration of 1.5x10^<21> cm^<-3> with a resistivity of 1.9x10^<-4> OMEGAcm has been obtained, which is the highest hole concentration for GaAs reported so far. Furthermore, carbon was found to be much less diffusive than other pーtype dopants, such as beryllium and zin c, even at extremely high doping levels. Therefore, carbon is a promising dopant for the HBT applications. However, at high doping levels, the lattice constant decreases with increasing carrier concentration, which creates a lattice mismatch between heavily carbon doped pーGaAs and moderately doped GaAs. To compensate this lattice mismatch, a small amount of indium was added to grow InGaAs. A hole concentration of 2.6x10^<20> cm^<-3> was obtained for InGaAs (In-5%) lattice matched to GaAs substrate. It was also found that the band-gap of carbon doped GaAs decreases with carrier concentration. Since this shrinkage is as large as 200 meV for a hole concentration of 5x10^<20> cm^<-3>, a pseudo-HBT has been proposed, which uses GaAs instead of AlGaAS for the emitter layer. In pseudo-HBTs, because of the band-gap shrinkage of heavily carbon doped GaAs in the base, a high emitter injection efficiency, and excellent high frequency performance can be expected, as in conventional HBTs. A pseudo-HBT with 100 nm thick base (p=1x10^<20> cm^<-3>) was fabricated and a DC current gain of 1.7 was obtained.