Creation of deep levels in horizontal Bridgman-grown GaAs by hydrogenation

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  • Creation of deep levels in horizontal Bridgmangrown GaAs by hydrogenationHoon Young Cho, Eun Kyu Kim, SukKi Min, Jae Boong Kim, and Jin Jang Citation: Applied Physics Letters 53, 856 (1988); doi: 10.1063/1.100094 View online: http://dx.doi.org/10.1063/1.100094 View Table of Contents: http://scitation.aip.org/content/aip/journal/apl/53/10?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Deep level defects in GaAs on Si substrates grown by atomic hydrogenassisted molecular beam epitaxy J. Appl. Phys. 80, 4770 (1996); 10.1063/1.363415 Deep levels in undoped horizontal Bridgman GaAs by Fourier transform photoconductivity and Hall effect J. Appl. Phys. 71, 246 (1992); 10.1063/1.350750 An evaluation of horizontal Bridgmangrown, undoped, semiinsulating GaAs J. Appl. Phys. 63, 4413 (1988); 10.1063/1.340185 Oxygen distribution in a horizontal Bridgmangrown, semiinsulating GaAs ingot Appl. Phys. Lett. 46, 391 (1985); 10.1063/1.95588 Passivation of the dominant deep level (EL2) in GaAs by hydrogen Appl. Phys. Lett. 41, 1078 (1982); 10.1063/1.93407

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    http://scitation.aip.org/content/aip/journal/apl?ver=pdfcovhttp://oasc12039.247realmedia.com/RealMedia/ads/click_lx.ads/www.aip.org/pt/adcenter/pdfcover_test/L-37/1940596036/x01/AIP-PT/Keysight_APLArticleDL_121714/en_keysight_728x90_3325-2Pico.png/47344656396c504a5a37344142416b75?xhttp://scitation.aip.org/search?value1=Hoon+Young+Cho&option1=authorhttp://scitation.aip.org/search?value1=Eun+Kyu+Kim&option1=authorhttp://scitation.aip.org/search?value1=SukKi+Min&option1=authorhttp://scitation.aip.org/search?value1=Jae+Boong+Kim&option1=authorhttp://scitation.aip.org/search?value1=Jin+Jang&option1=authorhttp://scitation.aip.org/content/aip/journal/apl?ver=pdfcovhttp://dx.doi.org/10.1063/1.100094http://scitation.aip.org/content/aip/journal/apl/53/10?ver=pdfcovhttp://scitation.aip.org/content/aip?ver=pdfcovhttp://scitation.aip.org/content/aip/journal/jap/80/8/10.1063/1.363415?ver=pdfcovhttp://scitation.aip.org/content/aip/journal/jap/71/1/10.1063/1.350750?ver=pdfcovhttp://scitation.aip.org/content/aip/journal/jap/63/9/10.1063/1.340185?ver=pdfcovhttp://scitation.aip.org/content/aip/journal/apl/46/4/10.1063/1.95588?ver=pdfcovhttp://scitation.aip.org/content/aip/journal/apl/41/11/10.1063/1.93407?ver=pdfcov

  • Creation of deep levels in horizonta~ Bridgman .. grown GaAs by hydrogenation

    Hoon Young Cho, Eun Kyu Kim, and Suk-Ki Min Semiconductor Materials Laboratory, Korea Advanced Institute of Science and Technology, P. 0. Box 131, Cheongryang, Seoul 130-650, Korea

    Jae Boong Kim and Jin Jang Department afPhysics. Kyung Hee University, Dongdaemoon-ku, Seoul 131-701, Korea

    (Received 8 April 1988; accepted for pUblication 27 June 1988)

    The effect of hydrogen plasma exposure on the deep levels in GaAs grown by the horizontal Bridgman method was studied. After hydrogenation at 250 DC for 3 h, the concentrations of the electron deep levels, such as the EL2 trap (Ee - OJH eV), the EL3 trap (E, - 0.63 eV), and the EL6 trap (Ee - 0.35 eV), decrease by one order of magnitude. On the other hand, three new electron traps at Ee - 0.42 eV, Ec - 0.54 eV, and Ee - 0.94 eV are created. After rapid thermal annealing up to 550C for 10 s, these created traps are reduced and the deep levels decreased by hydrogenation recover nearly completely. This result reveals that the passivation and creation of deep levels by hydrogenation may be explained as the interaction of atomic hydrogen with an unsaturated bond of native defects.

    It has been demonstrated that atomic hydrogen, pro-duced by plasma hydrogen, can passivate a variety of defects and impurity levels in semiconductors. 1- 7 Passivation and annealing recovery were reported for the three dominant deep levels in GaAs.-P ) These are the EL2 trap at E, - 0.82 eV, the EL3 trap at E, - 0.54 eV, and the EL6 trap at Ec - 0.36 eV. Annealing recovery of these deep levels does not

    begin until 500 "C," several hundred degrees higher than for shallow levels, and the possibility of other compensating de-fects created by atomic hydrogen has been ruled out. How-ever, there is still debate ahout the recovery of deep levels by thermal annealing and the creation of new deep levets during hydrogenation. While it is obvious that atomic hydrogen is involved in the passivation mechanism, 1-9 the microscopic origin is stili unclear, and there is no report on the creation of deep levels by hydrogen incorporation so faL lo

    Figure 1 shows the change of the deep levels effected by hydrogen plasma exposure at 250 cC for undoped GaAs. The concentrations of the EL2 trap eE, - 0.82 eV), the EL3 trap (Ee ~- 0,54 eV), and the EL6 trap (Ee - 0.35 eV) as typical hulk deep levels were in the range of5-8 X 1015 cm- 3

    for as-grown GaAs. After hydrogenation at 250C for 3 h, the concentrations of the EL2, and the EL3, and the EL6 traps decrease greatly and the signal of the EL6 trap at around 165 K shows a broad peak at 175 K. By using the DLTS signal analysis method,11 it is confirmed that the broad signal at 175 K involves two overlapped peaks, which

    In this letter we report, for the first time, the creation of three deep levels in un doped horizontal Bridgman (HB) GaAs by hydrogen plasma exposure. These new traps do not appear in Si-doped GaAs (2.DX 1017 cm- ') even after hy-drogen plasma exposure.

    A GaAs bulk crystal with a 1.4 X 10 16 cm- 3 carrier con-centration grown by the HB method has been used. Hydro-gen plasma exposure was carried out at 250C in a capaci-tively coupled plasma-enhanced chemical vapor deposition (CVD) reactor. The hydrogen pressure during the dis-charge was 0.57 Torr and the discharging power density 0.06 W /cm2 Hydrogenated GaAs samples were annealed by rap-id thermal process ( RTF) at the given temperatures for lOs. Before fabricating Schottky diodes, surface layers of 0.5 pill thickness were chemically etched in order to remove the front damaged layer. A Au Schottky diode with a diameter of 0.5 mm was fabricated using a thermal evaporator. The activation energy, the capture cross section, and the concen-tration of each trap were obtained using a deep level tran-sient spectroscopy (DLTS) system interfaced to HP 310 mi-crocomputer. We used a 1 MHz capacitance meter (HP 4280A) and a pulse generator (RP 80l1A) to measure the D L TS signal.

    I

    1- - ~ ~

  • represent two electron deep levels at Ee - 0.35 eV with a capture cross section of 1.3 X 10 15 cm2 and at Ee -- 0.42 cV with a capture cross section of5.3 X 10- 15 cm2 , respectively. Because the 0.35 eV trap is a native deep level before hydro-genation, the 0.42 eV trap, denoted as the EN3 trap in this letter, is newly created. Another new trap that peaked at 285 K, denoted as the EN2 trap (Ee - 0.54 eV), was created. This trap is not a member of the EL2 family. A peak at 410 K, denoted as the EN 1 trap (Ec -- 0.94 e V), can also he seen from Fig. 1 after hydrogenation. As a result, after 3 h hydro-genation, the created deep levels are the ENl trap (Ee - 0.91 eV), the EN2 trap (Ee - 0.54 eV), and theEN3 trap (Ee - 0.42 eV). The three kinds of new traps have ap-peared after 3 h hydrogen plasma exposure for undoped HB-grown GaAs produced by Sumitomo Co. as well as for our un doped samples. But we cannot find these new traps in Si-doped GaAs.

    Figure 2 shows the concentration of the created deep levels in hydrogenated GaAs as a function of depth from the surface, After hydrogenation at 250 OC for 3 h, the EL2, the EL3, and the EL6 traps were reduced greatly. Particularly, the concentration of the EL2 trap decreased by the one order of magnitude up to 1.5 pm from the surface. On the other hand, the concentrations of the EN 1, the EN2, and the EN3 traps decrease with depth from the surface.

    Figure 3 shows the changes of deep levels by hydrogena-tion and the recovery of the deep levels by R TP in undoped GaAs. After annealing at 550C for 10 s, the new traps creat-ed after hydrogenation are almost removed. The concentra-tion of the created new traps decreases with increase of the annealing temperature up to 550C, On the contrary, the decreased EL2, EL3, and EL6 traps were recovered into the original quantity after 550C annealing. We can see similar relative changes in the concentration of the EL and EN traps by R TP even though the EN traps decrease and the EL traps increase.

    We could not observe the new deep levels in doped GaAs after hydrogenation, since the detection limit of deep

    M , E v

    10 16

    >-f- 10'" lfl z W C

    0..

    ~ 1014 t-

    0.0 0.5 1.0 1.5 2.0

    DEPTH (;.1m)

    FIG. 2. Concentration profiles of the deep levels in hydrogenated HB GaAs for 3 h as a function of depth from the surface.

    657 Appl. Phys. Lett., Vol. 53, No.1 0,5 September 1988

    RTA 10 see.

    as-hydrogenated

    ~l ! ~ I

    as-grown

    ~--::J EL2

    ELG EL3

    ~ ~EN2 ~EN3

    300 400 500 600

    ANNEALING TEMPERATURE (oC)

    FIG. 3. Effect of hydrogenation and annealing on the deep trap denSEly in undoped HR GaAs. Rapid thermal annealing was done for \0 s.

    levels in doped GaAs is much lower than that of un doped GaAs. One might argue that the created deep levels might be due to plasma-induced damage during the hydrogen plasma exposure in undoped GaAs, but we could not observe the EN group defect after nitrogen plasma damage. Note that the plasma power density during the hydrogen discharge is low enough (0.06 W /cm2 ). Therefore, it appears that the creat-ed EN traps are due to hydrogen incorporation in undoped HB GaAs during hydrogenation.

    The decrease of the native deep levels (the EL group) is believed to be the neutralization of active states of them by atomic hydrogen. Especially, if the structure of the EL2 trap, as we proposed,12,n is VAs As] VOa ASOa' the passiva-tion of the EL2 trap is able to be explained as the bonding interaction of atomic hydrogen with the unsaturated inter-stitial atom (-~-As]--) or an antisite C-AsOa) of the EL2 structure. Taking into account these structures, it is likely that the created deep levels are hydrogen complexes asso-ciated with EL group deep levels during hydrogenation. The recovery of the native deep levels by thermal annealing is due to the outdiffusion of the bonded atomic hydrogen from the hydrogen complexes. Although the new deep levels were created by hydrogenation, the passivation of the EL group deep levels may be a benefit in the GaAs devices because the total concentration of deep levels is decreased to about one-tenth as less as before.

    In summary, we demonstrated that the three deep lev-els, at Ee - 0.42 eV, Ee - 0.54 eV, and Ee - 0.94 eV, are

    Cho eta/. 857

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  • created after hydrogen plasma exposure in undoped HB GaAs and these created deep levels are reduced after rapid thermal annealing up to 550C for 10 s. We proved ihat the creation and the recovery of deep levels arise from the incor-poration of hydrogen, not from hydrogen plasma damage.

    The authors wish to thank S. C. Park and C. W. Han for preparing thc HB GaAs samples, as well as C. K. Kim for experimental assistance.

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