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Measurements have been made of the transit times of pulses of 30-MHz longitudinal and transverse ultrasonic waves in sulfur-doped n-type single crystals of GaSb and GaP down to 4.2 K.Length-versus-temperature measurements have been made for GaP between 80 and 300 K using a silica dilatometer. Values are presented for the elastic constants C;, at various temperatures. The C;" for GaP below room temperature are the first ever reported. From the low-temperature elastic constants are deduced elastic Debye temperatures of 269.4 K for GaSb and 443.8 K for GaP. Martin's relation between the elastic constants is found to be satisfied no better when the "harmonic" elastic constants rather than room-temperature data are used in it. The temperature dependence of each C, , of GaSb and GaP can be fitted in most of our temperature range by a function having the form suggested byLeibfried and Ludwig to account for lattice anharmonicities. The function contains the average energy of a harmonic lattice oscillator multiplied by a factor K;, whose value is chosen to yield agreement with data at 240 and 4.2 K. For GaSb the value of K» is accounted for mainly by a term containing the thermal expansion, the pressure derivative of Ci"and the bulk modulus; whereas K ll and K44 each has a much larger value than can be attributed to the thermal-expansion term. Data on other semiconductors are reviewed and it is found that K» & K» p K4, for all III-V semiconductors for which suAicient data are available.

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