Spatially resolved characterization of HgCdTe materials and devices by scanning laser microscopy

Abstract

Spatially resolved characterization of HgCdTe materials and p-n junction diodes using scanning laser microscopy is reviewed. Several techniques that yield spatial maps of electrical inhomogeneities in HgCdTe material and non-uniformities in various performance parameters of p-n junctions fabricated using these materials have been developed. Many of the techniques are non-destructive, or can be made such with minor changes in sample preparation, and are scalable to large full wafers. A high-resolution and nondestructive techniquecalled'laserbeam inducedcurrent(~61c)'hasbeendeveiopedforspatial mapping of electrically active regions in HgCdTe. When applied to unprocessed HgCdTe material, LBIC images represent spatial distributions of electrically active defects including inclusions, strain. damage, precipitates. stacking faults, twin boundaries, dislocation clusters, bandgap and doping variations. Device structures such as p-n junctions are special cases of electrically active regions, therefore the LBIC technique lends ibeif to a nondestructive study of p n junction arrays without requiring any direct electrical contact to the individual elements of the array. The remote contacting, especially using pressure contacts, makes the application of the LBIC technique nondestructive, allowing testing at various stages of device processing to identify particular processing procedures that need optimization. LBIC has also been used to spatially map electrical non-uniformities at the HgCdTe surface near its interface with an insulating passivation layer. Besides LBIC imaging, scanning laser microscopy has been used for several other applications. For HgCdTe p-n junctions, applications include photoresponse mapping (uniformity, active area and diffusion length determination, contact bonding effects), spatially resolved light-induced degradation, and avalanche photodiode properties (ionization coefficients. localized breakdown). A key technique currently in development is the non-contact diode R d determination based on trapping mode photoconductivity. Examples of scanning laser microscopy on HgCdTe materials are infrared transmission mapping (thickness and bandgap variations), photoluminescence mapping, and minority carrier lifetime mapping (distribution of recombination centres).

Junction depth measurement in HgCdTe using laser beam induced current (LBIC)

“…7 Implanted p-n junction depths are one important device parameter that influences the yield, uniformity and operability of fabricated IRFPAs. Variations in junction depth over the array area may require correction in the post-detection signal processing.…”

“…7 This is because in testing, the detector arrays are mated to silicon read-out electronics by flip-chip hybrid bonding and measured at cryogenic temperatures (~80K). There is, therefore, potential for nondestructive testing techniques that could be applied at intermediate processing stages to monitor the fabrication processes, particularly after the junction formation step.…”

“…LBIC has proven useful in providing spatially resolved information about electrically active defects and localized nonuniformities in HgCdTe materials and devices used for infrared photovoltaic arrays. [7][8][9] In LBIC, regions of the semiconductor material which contain built-in fields will separate electron-hole pairs generated by an incident low power focused laser beam providing a measurable current. By scanning the laser across the sample, a map of the induced current is obtained which is indicative of the localized electric field distributions in the semiconductor.…”

“…Device structures such as p-n junctions are special cases of electrically active regions and therefore the LBIC technique lends itself to a study of p-n junction arrays while requiring no direct contact to the individual elements of that array. 7 The spatial LBIC profile of p-n junctions is dependent upon a multitude of physical semiconductor parameters. The extraction of some of these parameters, such as junction doping density and minority carrier lifetime, is possible using LBIC.…”

Mercury cadmium telluride implanted junction profile measurement and depth control

“…ME uctive optical vices. [12] laser which i dering an N-ty and hence carr wept across int ential volume, is results in a of minority c ation of the ph h the two remo d is dependen metrically cent oint across the tes from the ce ro LBIC signa ection of the e tion is shown lanar PN junc for the bound nt ction depth be ed by transfor commonly ad perty of HgCd is focused on ype well in a riers are gener to the N-regio , the excess ho non-uniform carriers into th hoto-generated ote contacts a nt on the posit tral position e junction, whi enter of the ju al. At the two lectric field in in Fig.1.…”