Dec 25, 2019

Determination of Shallow Acceptor Concentration in  SI  ‐ GaAs from Steady‐State and Transient Microwave Photoconductivity Measurements

A non‐destructive characterization method using microwaves has been employed to determine the shallow acceptor concentration in undoped LEC semi‐insulating gallium arsenide  wafers. Both the above‐bandgap steady‐state and the below‐bandgap transient photoconductivities of  wafers are measured using a Ka‐band reflection‐type microwave setup in which there is no need to fabricate electrical contacts on  wafers. A photoconductivity model adopted from the two‐energy‐level defect model for undoped LEC semi‐insulating  is used to derive the relationship between the photoinduced microwave response and the concentration of shallow acceptors, mainly carbon. In the above‐ bandgap photoconductivity measurement, it is found that the steady‐state microwave response is inversely proportional to the square root of the shallow acceptor concentration. In the below‐bandgap photoconductivity measurement, the transient microwave response shows an initial fast decay and a second slower decay which has a Na‐related decay time constant. More than 30 undoped LEC  bulk wafers were used in our measurements to establish the correlation. These wafers have a carbon concentration ranging from  to , determined by LVM infrared absorption. Good agreements have been found between the shallow acceptor concentration obtained from the microwave photoconductivity measurements and the LVM carbon concentration.


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