Robert Andrews Millikan (March 22, 1868 – December 19, 1953) was an American experimental physicist honored with the Nobel Prize for Physics in 1923 for the measurement of the elementary electronic charge and for his work on the photoelectric effect.
Heinrich Rudolf Hertz (] ; 22 February 1857 – 1 January 1894) was a German physicist who first conclusively proved the existence of the electromagnetic waves theorized by James Clerk Maxwell's electromagnetic theory of light.
 The unit of frequency — cycle per second — was named the "hertz" in his honor.
A photocathode is a negatively charged electrode in a light detection device such as a photomultiplier or phototube that is coated with a photosensitive compound.
 When this is struck by a quantum of light (photon), the absorbed energy causes electron emission due to the photoelectric effect.
An avalanche photodiode (APD) is a highly sensitive semiconductor electronic device that exploits the photoelectric effect to convert light to electricity.
 APDs can be thought of as photodetectors that provide a built-in first stage of gain through avalanche multiplication.
 From a functional standpoint, they can be regarded as the semiconductor analog to photomultipliers. By applying a high reverse bias voltage (typically 100–200 V in silicon), APDs show an internal current gain effect (around 100) due to impact ionization (avalanche effect).
 However, some silicon APDs employ alternative doping and beveling techniques compared to traditional APDs that allow greater voltage to be applied (> 1500 V) before breakdown is reached and hence a greater operating gain (> 1000).
 In general, the higher the reverse voltage, the higher the gain.
 Among the various expressions for the APD multiplication factor ("M"), an instructive expression is given by the formula
Stoletov's law (or the first law of photoeffect) for photoelectric effect establishes the direct proportionality between the intensity of electromagnetic radiation acting on a metallic surface and the photocurrent induced by this radiation.
 The law was discovered by Aleksandr Stoletov in 1888.
The history of quantum mechanics is a fundamental part of the history of modern physics.
 Quantum mechanics' history, as it interlaces with the history of quantum chemistry, began essentially with a number of different scientific discoveries: the 1838 discovery of cathode rays by Michael Faraday; the 1859–60 winter statement of the black-body radiation problem by Gustav Kirchhoff; the 1877 suggestion by Ludwig Boltzmann that the energy states of a physical system could be "discrete"; the discovery of the photoelectric effect by Heinrich Hertz in 1887; and the 1900 quantum hypothesis by Max Planck that any energy-radiating atomic system can theoretically be divided into a number of discrete "energy elements" "ε" (epsilon) such that each of these energy elements is proportional to the frequency "ν" with which each of them individually radiate energy, as defined by the following formula:
In 1922, Albert Einstein was awarded the 1921 Nobel Prize in Physics, "for his services to Theoretical Physics, and especially for his discovery of the law of the photoelectric effect".
 This refers to his 1905 paper on the photoelectric effect, "On a Heuristic Viewpoint Concerning the Production and Transformation of Light", which was well supported by the experimental evidence by that time.
 The presentation speech began by mentioning "his theory of relativity [which had] been the subject of lively debate in philosophical circles [and] also has astrophysical implications which are being rigorously examined at the present time".
Albert Einstein (14 March 1879 – 18 April 1955) was a German-born theoretical physicist.
 Einstein developed the theory of relativity, one of the two pillars of modern physics (alongside quantum mechanics).
 Einstein's work is also known for its influence on the philosophy of science.
 Einstein is best known by the general public for his mass–energy equivalence formula "E" = "mc" (which has been dubbed "the world's most famous equation").
 He received the 1921 Nobel Prize in Physics "for his services to theoretical physics, and especially for his discovery of the law of the photoelectric effect", a pivotal step in the evolution of quantum theory.
A digicon detector is a spatially resolved light detector using the photoelectric effect directly.
 It uses magnetic and electric fields operating in a vacuum to focus the electrons released from a photocathode by incoming light onto a collection of silicon diodes.
 It is a photon-counting instrument, so most useful for weak sources.
The photoelectric effect is the emission of electrons or other free carriers when light is shone onto a material.
 Electrons emitted in this manner can be called "photo electrons".
 The phenomenon is commonly studied in electronic physics, as well as in fields of chemistry, such as quantum chemistry or electrochemistry.

Question: What German born physicist discovered the photoelectric effect in1887?
Answer: Heinrich Hertz