A p-Ge C n-Si Heterojunction Diode Grown by Molecular Beam Epitaxy

A

p-Ge /n-Si Heterojunction Diode Grown by Molecular Beam Epitaxy

Xiaoping Shao,S.L.Rommel,Student Member,IEEE ,B.A.Orner,Student Member,IEEE ,

J.Kolodzey,Senior Member,IEEE ,and Paul R.Berger,Senior Member,IEEE

Abstract—We report on the fabrication and characterization of the first p-n diode made from a heterojunction of epitaxial p-type Ge 0:998C 0:002on an n-type Si substrate.Epitaxial Ge 0:998C 0:002was grown on a (100)Si substrate by solid source molecular beam epitaxy.The p-GeC/n-Si junction exhibits diode rectification.The I-V characteristics of the p-GeC/n-Si diode indicate a reasonable reverse saturation current of 89pA/ m 2at 01V and a high reverse breakdown voltage in excess of 040V.Photoresponse from the Ge 0:998C 0:002p-n diode was observed from 1.3- m laser excitation resulting in an external quantum efficiency of 1.4%.

I.I NTRODUCTION

G

ROUP IV semiconductor alloys have attracted intense studies over the last decade for their potential ap-plications in electronic as well as optoelectronic integrated circuits on Si [1]–[2].Due to the 4.2%lattice mismatch between Si and Ge,most investigations have involved SiGe heterostructures with limited Ge concentration

(

Ge ,by adding C to the SiGe system,makes

it possible to reduce the strain within the SiGeC system about the lattice matching condition for Si substrates while allowing adjustable bandgaps [4]–[6]by altering the Ge:C ratio.The binary alloy

Ge also provides the same flexibility from pure Ge under compressive strain (4.2%misfit)to diamond under tensile strain (

C

atoms/cm

C

C -Si wafer

with a carrier concentration of 10cm by MBE in an EPI 620system without a buffer layer.Details of the

Ge

growth are described elsewhere [8].The substrate temperature during growth was kept at 400

m.The C concentration was

0.2%,as determined by the growth condition,calibrated from samples with higher C concentrations.The

Ge

C epilayer was doped p-type by a concur-rent boron flux,using an effusion cell loaded with pure boron in a pyrolytic graphite crucible during the MBE growth.From Hall effect measurements,the electrically active B concentra-tion was

about cm .The

Ge epilayer was also examined in a Philips 400T transmission electron microscope (TEM)in cross sectional views.The TEM specimen was prepared by mechanical thinning followed by Ar ion milling at a voltage of 4kV.

Heterojunction p-n diodes were fabricated and a schematic is shown in the insert of Fig.1.Circular GeC mesas were formed by photolithography and then etching down to the Si substrate,using a

H :H :H

m .S t a n d a r d

l i f t o f f t e c h n o l o g y w a s u s e d t o f o r m

-b e a m e v a p o r a t i o n o f T i /A u o n t h e e n t i r

o f t h e s u b s t r a t e .T h e s a m p l e s w e r e a n n e a l e d a

-

N

.

0741–3106/97$0.00©1997I E E E