- Email: [email protected]
Photoluminescence spectra of Ga-doped and Al-doped 4H-SiC
vi
ABSTRACTS OF ARTICLES TO APPEAR IN J. PHYS. CHEM. SOLIDS F.K. Lotgering and A.M. van Diepen, Philips Research Laboratories, Eindhoven, The Netherlands.
MOssbauer spectra were obtained of the paramagnetic spinels Zn2~I Zn~_Xy2Ti~t+X),2Fe~X Fe~104 and susceptibilities were measured.2~ The differencedue and strong Fe3~spectrum, between the paramagnetic Fe to the different quadrupole splitting, is used for the distinction between the two species. At 300 K a superposition of the Fe3~and the Fe2~spectra is found for most of the iron and, in addition, some continuous absorption. The latter is strongest for equal Fe3~and Fe2~concentration (x = 1/2) while it disappears towards the end members (Fe3~only or Fe2~only) as well as with decreasing temperature (between 78 and 200K). From this it is concluded that it arises from thermally activated electron exchange, the frequency of which passes a “critical” value of lO8sec’ for increasing temperature. Paramagnetic susceptibilities are found to obey a Curie— Weiss law down to low temperatures. From the dependence of the asymptotic Curie temperature on the composition the magnetic interaction parameters J 11 =3~—Fe3~, 1.4K,Fe2~—Fe2~ .122 = —33and K and .i12 = + Fe3~—Pe2~ ~1.6 K for theare Federived. The experimental results are interactions discussed in terms of a hopping model with an activation energy q ~ 0.12 eV and a non-equivalence ofthe octahedral sites expressed by a varying potential energy difference U 0 between neighbouring sites. The continuous absorption at 300 K for x = 1/2 is attributed to about 17% of the iron on sites with 3~, ~Jorunning from 0 Fe~interaction to 0.06 eV. The ferromagnetic Fe (J 12) is attributed to electron via transfer fromintegral localized 2~ions to Fe3~neighbours a transfer b 0f Fe the order of 0.05 eV. The magnitudes of J 12 and b are tentatively explained, Received 30August 1976 —
5
ELECTRONIC ENERGY BAND PARAMETERS OF GRAPHITE AND THEIR DEPENDENCE ON PRESSURE, TEMPERATURE AND ACCEPTOR CONCENTRATION R.O. Dillon and IL. Spain, Laboratory for High Pressure Science, Department of Chemical Engineering, University of Maryland, College Park, MD 20742, U.S.A.; and J.W. McClure, Department of Physics, University of Oregon, Eugene, OR 97403, U.S.A.
Vol.21, No.7
An analysis has been made of experimental data on the dependence of electronic properties of graphite on pressure and acceptor concentration, using the Slonczewski—Weiss dispersion relationship for the free carriers. it is shown that such experiments cannot be adequately interpreted without in taking into account all of the band-overlap parameters Previous workers had particularly neglected this the theory. influence of the parameter y~,which trigonally warps the constant energy surfaces. The results presented will also be useful for interpreting new experiments in which either the band overlap parameters or the Fermi-energy are changed. A discussion of possible changes in band parameters with temperature is included. Received 28 June 1976 Revised 29 October 1976 6
PHOTOLUMINESCENCE SPECTRAOF Ga-DOPED AND Al-DOPED4H-SiC A. Suzuki, H. Matsunami and T. Tanaka, Department of Electronics, Faculty of Engin-
Kyoto University, Kyotoof 606, Japan. Blueeenng, and violet photoluminescences Ga-doped and Al-doped 4H-SiC single crystals grown from a Si melt have been studied at 2—200K. Luminescence spectra under continuous excitation and their dependences on temperature and excitation intensity as well as temperature dependence of the luminescence intensity are measured. Time-resolved spectra and decay curves after pulsedThe excitation also areatobserved at various peratures. luminescences 2 K are found to beterndue to pair recombination N donorThe introduced unintentionally and thebetween Ga or Altheacceptor. spectra of the two samples resemble each other in shape, and each consists of a zero-phonon peak and its phonon replicas. At higher temperatures, another emission appears due to the recombination of free electrons with bound holes at the acceptors in place of the pair emission. From the energies of the zero-phonon peaks of these two kinds of emissions, the ionization energies of the Ga and the Al acceptors are determined to be 249 ± 3meV + E~and 168 ±3 meV + E~,respectively, where E~is the exciton binding energy of 4H-SiC, and that of the N donor is estimated to be 55 ±7meV using an appropriate approxmiation. Received 28 June 1976 Revised 15 October 1976
ABSTRACTS OF ARTICLES TO APPEAR IN J. PHYS. CHEM. SOLIDS F.K. Lotgering and A.M. van Diepen, Philips Research Laboratories, Eindhoven, The Netherlands.
MOssbauer spectra were obtained of the paramagnetic spinels Zn2~I Zn~_Xy2Ti~t+X),2Fe~X Fe~104 and susceptibilities were measured.2~ The differencedue and strong Fe3~spectrum, between the paramagnetic Fe to the different quadrupole splitting, is used for the distinction between the two species. At 300 K a superposition of the Fe3~and the Fe2~spectra is found for most of the iron and, in addition, some continuous absorption. The latter is strongest for equal Fe3~and Fe2~concentration (x = 1/2) while it disappears towards the end members (Fe3~only or Fe2~only) as well as with decreasing temperature (between 78 and 200K). From this it is concluded that it arises from thermally activated electron exchange, the frequency of which passes a “critical” value of lO8sec’ for increasing temperature. Paramagnetic susceptibilities are found to obey a Curie— Weiss law down to low temperatures. From the dependence of the asymptotic Curie temperature on the composition the magnetic interaction parameters J 11 =3~—Fe3~, 1.4K,Fe2~—Fe2~ .122 = —33and K and .i12 = + Fe3~—Pe2~ ~1.6 K for theare Federived. The experimental results are interactions discussed in terms of a hopping model with an activation energy q ~ 0.12 eV and a non-equivalence ofthe octahedral sites expressed by a varying potential energy difference U 0 between neighbouring sites. The continuous absorption at 300 K for x = 1/2 is attributed to about 17% of the iron on sites with 3~, ~Jorunning from 0 Fe~interaction to 0.06 eV. The ferromagnetic Fe (J 12) is attributed to electron via transfer fromintegral localized 2~ions to Fe3~neighbours a transfer b 0f Fe the order of 0.05 eV. The magnitudes of J 12 and b are tentatively explained, Received 30August 1976 —
5
ELECTRONIC ENERGY BAND PARAMETERS OF GRAPHITE AND THEIR DEPENDENCE ON PRESSURE, TEMPERATURE AND ACCEPTOR CONCENTRATION R.O. Dillon and IL. Spain, Laboratory for High Pressure Science, Department of Chemical Engineering, University of Maryland, College Park, MD 20742, U.S.A.; and J.W. McClure, Department of Physics, University of Oregon, Eugene, OR 97403, U.S.A.
Vol.21, No.7
An analysis has been made of experimental data on the dependence of electronic properties of graphite on pressure and acceptor concentration, using the Slonczewski—Weiss dispersion relationship for the free carriers. it is shown that such experiments cannot be adequately interpreted without in taking into account all of the band-overlap parameters Previous workers had particularly neglected this the theory. influence of the parameter y~,which trigonally warps the constant energy surfaces. The results presented will also be useful for interpreting new experiments in which either the band overlap parameters or the Fermi-energy are changed. A discussion of possible changes in band parameters with temperature is included. Received 28 June 1976 Revised 29 October 1976 6
PHOTOLUMINESCENCE SPECTRAOF Ga-DOPED AND Al-DOPED4H-SiC A. Suzuki, H. Matsunami and T. Tanaka, Department of Electronics, Faculty of Engin-
Kyoto University, Kyotoof 606, Japan. Blueeenng, and violet photoluminescences Ga-doped and Al-doped 4H-SiC single crystals grown from a Si melt have been studied at 2—200K. Luminescence spectra under continuous excitation and their dependences on temperature and excitation intensity as well as temperature dependence of the luminescence intensity are measured. Time-resolved spectra and decay curves after pulsedThe excitation also areatobserved at various peratures. luminescences 2 K are found to beterndue to pair recombination N donorThe introduced unintentionally and thebetween Ga or Altheacceptor. spectra of the two samples resemble each other in shape, and each consists of a zero-phonon peak and its phonon replicas. At higher temperatures, another emission appears due to the recombination of free electrons with bound holes at the acceptors in place of the pair emission. From the energies of the zero-phonon peaks of these two kinds of emissions, the ionization energies of the Ga and the Al acceptors are determined to be 249 ± 3meV + E~and 168 ±3 meV + E~,respectively, where E~is the exciton binding energy of 4H-SiC, and that of the N donor is estimated to be 55 ±7meV using an appropriate approxmiation. Received 28 June 1976 Revised 15 October 1976