Thermionic emission cooling in single barrier heterostructures

Abstract

Nonisothermal transport in InGaAsP-based heterostructure integrated thermionic coolers is investigated experimentally. Cooling on the order of a degree over 1 m thick barriers has been observed. This method can be used to enhance thermoelectric properties of semiconductors beyond what can be achieved with the conventional Peltier effect. © 1999 American Institute of Physics. ͓S0003-6951͑99͒02701-1͔Temperature stabilization of optoelectronic components ͑lasers, filters, switches, etc.͒ is of increasing importance in many high-speed and wavelength division multiplexed fiberoptics communication systems. Heat generation and thermal management in very large scale integrated ͑VLSI͒ circuits is becoming one of the barriers to further increase clock speeds and decrease feature sizes. Solid-state coolers integrated with devices are an attractive way to solve some of these problems. This means alternatives to thermoelectric cooling using Bi 2 Te 3 , the current industry standard, must be found. A solution is to use thermionic emission in heterostructures, a technique that can give significant cooling in conventional materials such as AlGaAs, InGaAsP, or SiGe. 1,2 In this letter, we investigate experimentally nonisothermal electron transport in InGaAsP-based heterostructure integrated thermionic ͑HIT͒ coolers.The conventional thermoelectric effect is based on bulk properties of materials. 3 When electrons flow from a material in which they have an average transport energy smaller than the Fermi energy to another material in which their average transport energy is higher, they absorb thermal energy from the lattice and this will cool down the junction between two materials. In an alternative method, thermionic emission current in heterostructures can be used to achieve evaporative cooling by selective emission of hot electrons over a barrier layer from cathode to anode. 1,2,4,5 Since the energy distribution of emitted electrons is almost exclusively on one side of the Fermi energy, upon the current flow, strong carriercarrier and carrier-lattice scatterings tend to restore the quasiequilibrium Fermi distribution in the cathode by absorbing energy from the lattice, and thus, cooling the emitter junction.In order to investigate experimentally thermionic emission cooling in heterostructures, a single InGaAsP ( gap ϭ1.3 m͒ barrier surrounded by n ϩ -InGaAs cathode and anode layers was grown using metal organic chemical vapor deposition ͑MOCVD͒. Cathode and anode layer thicknesses were 0.3 and 0.5 m and they were doped to 3 ϫ10 18 cm Ϫ3 . The barrier layer had an n doping of 2 ϫ10 17 cm Ϫ3 and was 1 m thick. Mesas with an area of 90ϫ180 m 2 were etched down using dry etching techniques. Ni/AuGe/Ni/Au was used for top and bottom contact metallization. Figure 1 displays the measured temperature on the top and on the bottom of the device as well as the substrate temperature far away from the device as a function of current. All temperatures are relative to the value at zero current. The rise in substrate temperature is an indicatio...

Conservation of Lateral Momentum in Heterostructure Integrated Thermionic Coolers

“…Theoretical estimates [1,2,16] show that there is an optimal barrier width of the order of a few electron energy relaxation lengths and an optimum barrier height of the order of k B T, and that such heterostructure coolers can provide 20-30 o C cooling with KW/cm 2 cooling density. Since the operating currents for the device is very high (10 5 A/cm 2 ), non-ideal effects such as the Joule heating at the metal-semiconductor contact resistance, and the reverse heat conduction have limited the experimental cooling results to <1 o C [3]. There is another regime of operation in which electron transport is dominated by the multi barrier structure [10][11][12].…”

“…1) [1][2][3][4][5][6][7][8][9]. In these structures a potential barrier is used for the selective emission of hot electrons and evaporative cooling of the electron gas.…”

Characterization of Single Barrier Microrefrigerators at Cryogenic Temperatures

“…Therefore, the device achieves a greater cooling efficiency. [2][3][4] Typically, both bulk thermoelectric properties of the barrier material and evaporative thermionic emission from the cathode exist in a heterostructure integrated thermionic device. By varying the operating ambient temperature, one can alter the electron mean free path, to enhance ballistic transport, and thus observe the interplay between thermoelectric and thermionic contributions.…”

SiGeC Cantilever Micro Cooler

“…Thin film coolers that can be monolithically integrated with high speed, high power electronic and optoelectronic devices have been an active area of research [1][2][3].…”