CTU Prague RD50 Group

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1 CTU Prague RD50 Group Detector structures on GaAs (Mesa with Guard Rings) T. Horazdovský, D. Chren, Z. Kohout, M. Solar, B. Sopko ME CTU V. Jurka, E. Hulicius IP ASCR S. Pospisil IEAP CTU

2 Contents Motivation Structure of detectors Technology for GaAs detectors Results Conclusion References 2

3 Motivation The structure of detector on SI GaAs substrate was created using Schottky contact. The properties of the Schottky contact depend on metallization technology. The diffusion technology eliminate the influence of a substrate material on detector performance. For more stable properties we made the structure with PN junction (diffused or epi layer). 3

4 Motivation Diffusion solid-to-solid of Zn or MOCVD epi layer give us possibility to make ohmic contact on P+ side and give further possibility for research of detection structure. 4

5 Structure of the detectors SI GaAs substrate, thick. 500 um 1. P+ (Zn) junction depth (2 4 ) um Metallization of P+ (front) side : TiAu ( nm + 0 nm) Metallization of back side: AuGeNi (0+0+0)nm (Fig.1) 2. MOCVD epi layer P+ (C) thickn. 0,5 um MOCVD epi layer N+ (Si) back side Metallization of P+ and back side : TiAu ( nm + 0 nm) (Fig. 2, 3) or 5

6 Technology for GaAs detectors Diffused type deposition of SiO 2 + ZnO layers diffusion of Zn (solid to solid)- bellow 800 C, in FG removing of SiO 2 + ZnO layers making a ohmic contact on P+ and N+ side of structure (standard metallization : TiAu, AuGeNi, annealing 400 C in FG) separation of detector chips (cutting) - after cutting of the wafer to detector chips (5 x 5 mm) the sides of the chips was prepared by a special protectiv layer (Protection technology similar as for HV diodes) 6

7 Structure of the detectors TiAu P + (Zn) SI GaAs AuGeNi Fig.1:Vertical structure of detectors - diffusion type of structure 7

8 Technology for GaAs detectors MOCVD type without guard ring deposition of MOCVD epi layer (P+, dot. C) back side deposition of MOCVD epi layer (N+, dot. Si) making a ohmic contact on P+ and N+ side of structure (standard metallization : TiAu, AuGeNi, annealing 400 C in FG) separation of detector chips (cutting) - after cutting of the wafer to detector chips (5 x 5 mm) the sides of the chips was prepared by a special protectiv layer 8

9 Structure of the detectors TiAu MOCVD P + (C) SI GaAs N + TiAu epi (Si) Fig.2: Vertical structure of detectors - MOCVD epi type of structure 9

10 Technology for GaAs detectors MOCVD type with guard ring deposition of MOCVD epi layer (P+, dot. C) back side deposition of MOCVD epi layer (N+, dot. Si) making a ohmic contact on P+ and N+ side of structure - standard metallization : TiAu etching of the metallization to designed pattern following etching of GaAs (patterned metallization serves as etching mask) to form MESA structure This structure had not passivated surface

11 Structure of the detectors TiAu MOCVD P + (C) SI GaAs N + TiAu epi (Si) Fig.3: Vertical structure of detector with guard ring - MOCVD epi type of structure 11

12 Results I-V characteristic - diffused type,00 00,00 800,00 I [na] 600,00 400,00 0,00 0,00 0,00,00,00 30,00 40,00 50,00 60,00 70,00 80,00 90,00 0,00 U [V] 12

13 Results cip1 45V cip1 90V counts channel counts channel cip1 132V counts channel All presented spectra were measured using alpha-particle source Am 241 Pu

14 Results I-V characteristic - MOCVD type 800,00 700,00 600,00 500,00 I [na] 400,00 300,00 0,00 0,00 0,00 0,00,00 40,00 60,00 80,00 0,00 1,00 U [V] 14

15 Results cip2 47V cip2 91V counts channel counts channel cip2 133V counts channel 15

16 Results Fig.4: The photo of MESA type detectors with guard rings 16

17 Results I-V characteristic - MESA type (MOCVD) 16,00 14,00 12,00,00 I [na] 8,00 6,00 4,00 2,00 0,00 0,00 50,00 0,00 150,00 0,00 250,00 300,00 350,00 400,00 U [V] 17

18 Results 50V 150V counts channel counts channel 250V 350V counts channel counts channel 18

19 Conclusions Experiments show the ability of described technology to prepare functional detectors on GaAs The results show the MESA type has better leaking current in comparison with surface preserved type even the guard rings were not biased In near future we will study: - the influence of guard ring bias on the detector properties, - the spectra using gamma and rtg sources, - the influence of protective materials on I-V characterics 19

20 References 1. C.R.M.Grovenor: Structure of the Au/Ga As interface, EMIS Datareview RN=11126, September B.Tuck, T. Harrison: Diffusion of Zn in Ga As, EMIS Datareview RN=15150, February J.Ivančo at all: Semi-insulating Ga As based Schottky contacts for the detector of Ionising radiation: An effect of the interface treatment,6th International Workshop on GaAs and related compounds, Praha Průhonice, June 22-26, P.J.Selin at all : Characterisation of X-ray detectors fabricated from thick epitaxial Ga As NIM A 460 (01)

21 CTU Prague RD50 Group Thank you for your attention