For electronic applications, a series of boron-doped homoepitaxial diamond layers of high crystal quality have been grown on (100)-cut diamond substrates using the microwave plasma CVD method. The B-concentration varies from 3 x 1017 to 3 x lozo atoms/cm3. The layers are selectively grown into the shape of Hall bars using a sputtered SiOn mask. The diamond substrates are 3 x 3 x 1 mm3 in size. Gold wires are bonded to ohmic contacts on the Hall bars formed by an electron beam evaporated Mo/Pt/Au sandwich annealed at 950 "C for 30 min. Electrical characterization is performed in eight samples over the temperature range from 100 to 1300 K. The results arc discussed in detail. For diamond layers grown on synthetic nitrogen-doped (type Ib) substrates, current-voltage characteristics of diode type can be observed in the temperature range from 360 to 900 "C. Green electroluminescent light is emitted from the p-n junction area. High current Schottky diodes are also fabricated which consist of a gold contact to a moderately B-doped homoepitaxial layer grown on a synthetic heavily boron-doped (type I1 b) substrate. Fur elektronische Anwendungen wird eine Serie von Bor-dotierten homoepitaktischen Diamantschichten hoher kristalliner Gute auf (100)-geschnittenen Diamantsubstraten mittels der Mikrowellenplasma-unterstutzten CVD-Methode aufgewachsen. Die B-Konzentration variiert von 3 x 1017 bis 3 x lozo Atome/cm3. Die Schichten werden selektiv mittels gesputterter SiOz-Masken als Hallkreuze gewachsen. Die Diamantsubstrate sind 3 x 3 x 1 mm3 grof3. Golddrahtc werden an ohmsche Kontakte gebondet. Diese werden als Mo/Pt/Au-Schichtpakete mittels Elektronenstrahl-Aufdampfen und halbstundigem Tempern bei 950 "C hergestellt. Die elektrische Charakterisierung erfolgt bei acht Proben iiber den Temperaturbereich von 100 bis 1300 K. Die Ergebnisse werden eingehend diskutiert. Auf synthetischen Stickstoff-dotierten (Typ I b) Substraten werden Strom/ Spannungs-Charakteristikcn vom Diodentyp im Temperaturbereich von 360 bis 900 "C beobachtet. Grunes Elektrolumineszenzlicht wird von der p-n-Kontaktflache emittiert. Hochstrom-Schottkydioden werden ebenfalls hergestellt. Sie bestehen aus einem Goldkontakt zu einer m a i g B-dotierten homoepitaktischen Schicht, die auf einem synthetischen, hochdotierten (Typ I1 b) Substrat aufgewachsen wurde.T. H. BOWT and 0. WEIS EB = 0.37 eV, if moderately doped, and becomes metallic with EB = 0 eV for heavy d o p ing. Thus, suitably B-doped diamond can be used over a broad temperature range for p-type conduction. Substitutional single nitrogen atoms are donors [2] with an ionization energy EB = 1.7 eV which is too high for a utilizable n-type conduction at room temperature. At present, there is no n-type diamond available for applications at room temperature. Nevertheless, due to the exceptional physical properties of diamond [3], a variety of unusual electronic applications of semiconducting diamond are expected [4 to 61.Electronic diamond devices of high quality can only be demonstrated in monocrystalline...

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We report piezoelectric surface excitation of coherent acoustic 0.891-and 2.53-THz phonon pulses in quartz by means of chopped infrared laser radiation and the detection of these highly collimated phonons 10 mm from the excitation area using a superconducting tin bolometer. At 2.53 THz the effect of dispersion is clearly visible. Absorption of infrared photons in the bulk material generates incoherent phonons which also can be detected by the bolometers.We report in this paper first experiments showing the direct transformation, without change of frequency, of infrared laser radiation into phonon pulses by piezoelectric surface excitation 1 and, at higher frequencies, by one-phonon infrared absorption in quartz. These experiments are performed by focusing a chopped infrared-laser beam upon theX-cut face of a 10xl0xl0-mm 3 quartz cube kept in contact with liquid helium. In the case of piezoelectric phonon excitation the phonons are produced only at the surfaces; in the case of strong infrared absorption the phonon generation takes place in a thin layer near the surfaces. In order to get a time separation between laser radiation and phonon signal at the superconducting bolometer at the rear face, the laser-pulse duration should be 1 /j,sec or less. Since pulsed molecular lasers usually show an output radiation far too long for our purpose, an external beam chopper has been constructed 2 and inserted.Changing only gas fuel and some electrical parameters, laser emission can be observed in our setup at distinct frequencies between 337 (HCN) and 10.6 /im (C0 2 ). We report here only phononexcitation experiments using single emission lines at 0.891 THz (337-jum line 3 of HCN), at 2.53 THz (118-^m line 4 of H 2 0), and at 10.7 THz (28-/j,m line 5 of H 2 0). These lines were controlled by a compact external Michelson interferometer. Usually peak powers of about 10 W at 2.53 THz and of about 50 W at 10.7 THz are attainable. The insertion loss of the mechanical chopper is nearly 60% at 0.891 THz and less at higher frequencies.Our tin bolometers cover an area of 1 mm in diameter and have the shape of a meander. The stripe width as well as the free-space between the stripes is 0.1 mm. Vacuum deposition of the 600-800-A films is done with the substrate cooled to liquid-nitrogen temperature. Whereas these films are highly sensitive detectors for phonons, 6 only a very small fraction of incident infrared photons are absorbed as a consequence of the high electronic conductivity.Before discussing the experiments on coherent excitation, we give a rough estimate of the attainable power conversion from the incident electromagnetic wave into coherent phonons ("sound waves") at low frequencies where continuum acoustics can be applied. The method of piezoelectric surface excitation was introduced by Bommel and Dransfeld 7 for the generation of coherent phonon pulses in the gigahertz range. As Jacobsen 8 pointed out, the generation of sound in a piezoelectric crystal is due to the discontinuity of the piezoelectric stress at the surface ...

Thermal phonon radiators allow short pulses of incoherent thermal phonon beams to generate in a simple manner and the center frequency of the broad frequency distribution of the emitted phonons to vary up to the acoustic cutoff frequencies. This paper reports experimental investigations of the connection between radiation temperature and radiation power using films of several metals (copper, nickel, gold, and lead) as phonon radiators on diamond. The measured dependencies of the radiation temperature on the radiation power show that the radiation process is by far better described by assuming acoustic mismatch between radiator and transmission medium than using the model of perfect match. Some metals on diamond give a phonon radiation power of several kilowatts per square millimeter radiator area. With a diamond substrate held at liquid-helium temperature, a radiation temperature of a few hundred degrees Kelvin was achieved. If the phonon radiator deposited on diamond is immersed in liquid helium, the transport of heat to the liquid helium becomes important at radiation temperature below 30 °K and is dominant below 20 °K. This effect can be explained by assuming a thin vapor layer between the hot radiator and the liquid helium, and a gas kinetic energy transfer.